[U-Boot] Selectable / delayed initialization
Hi,
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
Later when it becomes clear that USB and Ethernet are needed we want to init those also. I suppose the easiest way of describing this is that we want to have some 'level 0' init, then perhaps move to level 1 and init peripherals at that level, then perhaps to level 2, etc. Quite often we will only get to level 1 before jumping to the kernel.
At the moment the U-Boot init code is spread around a bit - there are files called board.c within arch/xx/cpu/, board/xx/ and arch/xx/lib/. So it is hard to make this change just within a board file. Some other files have big lists of init calls like stdio.c and serial.c.
I am thinking of creating a way of specifying a list of peripherals which should be inited in each level, then moving all init code into a function which knows how to init each peripheral. Then we can call init_level(2) for example, to start up peripherals in that level. Perhaps level 0 would be reserved for pre-relocation init.
I am interested in any thoughts that people have about this and whether it might be implemented in a generally useful way. I am assuming that a driver registration / initcall approach would be a bridge too far for U-Boot at the moment, so I am thinking of a function with a big 'switch' statement.
The other related issue is that I notice that the arch/xxx/lib/board.c files are different but have a lot of common code. Is there some scope for starting a common/board.c file which slowly builds up common functionality so that over time we end up with only the architecture-specific code in the arch/lib/xxx/board.c? If so these these two goals could perhaps be progressed together.
Regards, Simon
Hi Simon,
On Wed, Aug 17, 2011 at 1:25 PM, Simon Glass sjg@chromium.org wrote:
Hi,
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
Later when it becomes clear that USB and Ethernet are needed we want to init those also. I suppose the easiest way of describing this is that we want to have some 'level 0' init, then perhaps move to level 1 and init peripherals at that level, then perhaps to level 2, etc. Quite often we will only get to level 1 before jumping to the kernel.
Well technically, the device init should only be done either
a) U-Boot core code needs to access the device (to read the environment for example) b) When a U-Boot command first uses the device b) When doing final init ready for the OS kernel
At the moment the U-Boot init code is spread around a bit - there are files called board.c within arch/xx/cpu/, board/xx/ and arch/xx/lib/. So it is hard to make this change just within a board file. Some other files have big lists of init calls like stdio.c and serial.c.
Yes, it is a mess
I am thinking of creating a way of specifying a list of peripherals which should be inited in each level, then moving all init code into a function which knows how to init each peripheral. Then we can call init_level(2) for example, to start up peripherals in that level. Perhaps level 0 would be reserved for pre-relocation init.
I am interested in any thoughts that people have about this and whether it might be implemented in a generally useful way. I am assuming that a driver registration / initcall approach would be a bridge too far for U-Boot at the moment, so I am thinking of a function with a big 'switch' statement.
I would prefer a device level 'start' and 'stop' hooks so when a command or the U-Boot core needs to use a particular device it calls device->start(), uses the device then calls device->stop(). Devices that are in use permanently (timers and console ports are prime examples), device->stop() is never called (or maybe called proir to entering the OS kernel). This would be a massive architectural change for U-Boot and leads into a 'driver framework'
The other related issue is that I notice that the arch/xxx/lib/board.c files are different but have a lot of common code. Is there some scope for starting a common/board.c file which slowly builds up common functionality so that over time we end up with only the architecture-specific code in the arch/lib/xxx/board.c? If so these these two goals could perhaps be progressed together.
Now that relocation has settled down and looks to be working in a much more platform independent manner, board_init_f() and board_init_r() should be able to be moved into /lib/ with any arch or board specific functionality carved out into init functions. Have a look at x86 and you'll see that board_init_f() and board_init_r() work in a very simlar manner to each other. I don't think this is going to be particularly difficult to implement. I am, however, still scratching my head trying to figure out how to create a simple mechanism for dynamic init sequence building (even if it is done at compile time). By this I mean a standard arch level init sequence and a way of allowing boards to insert init functions at arbitrary points in the init sequence without a mass of #ifdef's in /lib/board.c and without have each and every board having to define the whole init sequence in /board/init.c. At the moment it's done by reserving some specific points in the init sequence where U-Boot calls into the board-specific init functions. If the board has no need for such a call, it still needs to implement a do nothing stub function. I'm sure someone can come up with some clever pre-processor macro-foo to do something like this:
In board/foo.c:
int init_board_gpio() { /* Do Stuff */ } BOARD_INIT(init_board_leds, 214);
int init_board_leds() { /* Do Stuff */ } /* Init board LEDs after the boards GPIO has been initialised */ BOARD_INIT(init_board_leds, 215);
In arch/xxx/sdram.c
int init_sdram() { /* Do Stuff */ } /* SDRAM gets intialised really early (but not before timers) */ BOARD_INIT(init_sdram, 10);
In arch/xxx/<soc>/timer.c
int init_timers() { /* Do Stuff */ } /* Timers are needed early */ BOARD_INITinit_timers, 9);
You could even #define some of the steps with nice gaps between:
#define INIT_STEP_CPU 1 #define INIT_STEP_TIMERS INIT_STEP_CPU + 10 #define INIT_STEP_SDARM INIT_STEP_TIMERS + 10
But maybe it's all wishful thinking
Regards,
Graeme
Hi Graeme,
On Tue, Aug 16, 2011 at 11:42 PM, Graeme Russ graeme.russ@gmail.com wrote:
Hi Simon,
On Wed, Aug 17, 2011 at 1:25 PM, Simon Glass sjg@chromium.org wrote:
Hi,
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
Later when it becomes clear that USB and Ethernet are needed we want to init those also. I suppose the easiest way of describing this is that we want to have some 'level 0' init, then perhaps move to level 1 and init peripherals at that level, then perhaps to level 2, etc. Quite often we will only get to level 1 before jumping to the kernel.
Well technically, the device init should only be done either
a) U-Boot core code needs to access the device (to read the environment for example) b) When a U-Boot command first uses the device b) When doing final init ready for the OS kernel
At the moment the U-Boot init code is spread around a bit - there are files called board.c within arch/xx/cpu/, board/xx/ and arch/xx/lib/. So it is hard to make this change just within a board file. Some other files have big lists of init calls like stdio.c and serial.c.
Yes, it is a mess
I am thinking of creating a way of specifying a list of peripherals which should be inited in each level, then moving all init code into a function which knows how to init each peripheral. Then we can call init_level(2) for example, to start up peripherals in that level. Perhaps level 0 would be reserved for pre-relocation init.
I am interested in any thoughts that people have about this and whether it might be implemented in a generally useful way. I am assuming that a driver registration / initcall approach would be a bridge too far for U-Boot at the moment, so I am thinking of a function with a big 'switch' statement.
Well given your recent patch it seems this isn't a bridge too far :-) I would very much like init to be done via a registration macro as your patch does (and U-Boot commands already do). If we are going down that path I would even argue for a way to configure it at start-up (add/remove things).
I would prefer a device level 'start' and 'stop' hooks so when a command or the U-Boot core needs to use a particular device it calls device->start(), uses the device then calls device->stop(). Devices that are in use permanently (timers and console ports are prime examples), device->stop() is never called (or maybe called proir to entering the OS kernel). This would be a massive architectural change for U-Boot and leads into a 'driver framework'
That's great as far as it goes. But many devices have one-time initialization also. So perhaps
device->init() device->start() device->stop() device->start() device->stop() device->uninit()
although some might argue for open/close instead of start/stop.
As an example, USB typically requires some clock/pinmux setup after which it is ready for use. This happens at the beginning, often regardless of whether 'usb start' is ever used. While this might be against the grain, forcing all the init into the start() function then means that this code needs to check if the init was done in a previous start() call, and skip it if so. That seems wrong to me.
The other related issue is that I notice that the arch/xxx/lib/board.c files are different but have a lot of common code. Is there some scope for starting a common/board.c file which slowly builds up common functionality so that over time we end up with only the architecture-specific code in the arch/lib/xxx/board.c? If so these these two goals could perhaps be progressed together.
Now that relocation has settled down and looks to be working in a much more platform independent manner, board_init_f() and board_init_r() should be able to be moved into /lib/ with any arch or board specific functionality carved out into init functions. Have a look at x86 and you'll see that board_init_f() and board_init_r() work in a very simlar manner to each other. I don't think this is going to be particularly difficult to implement. I am, however, still scratching my head trying to figure out how to create a simple mechanism for dynamic init sequence building (even if it is done at compile time). By this I mean a standard arch level init sequence and a way of allowing boards to insert init functions at arbitrary points in the init sequence without a mass of #ifdef's in /lib/board.c and without have each and every board having to define the whole init sequence in /board/init.c. At the moment it's done by reserving some specific points in the init sequence where U-Boot calls into the board-specific init functions. If the board has no need for such a call, it still needs to implement a do nothing stub function. I'm sure someone can come up with some clever pre-processor macro-foo to do something like this:
In board/foo.c:
int init_board_gpio() { /* Do Stuff */ } BOARD_INIT(init_board_leds, 214);
int init_board_leds() { /* Do Stuff */ } /* Init board LEDs after the boards GPIO has been initialised */ BOARD_INIT(init_board_leds, 215);
In arch/xxx/sdram.c
int init_sdram() { /* Do Stuff */ } /* SDRAM gets intialised really early (but not before timers) */ BOARD_INIT(init_sdram, 10);
In arch/xxx/<soc>/timer.c
int init_timers() { /* Do Stuff */ } /* Timers are needed early */ BOARD_INITinit_timers, 9);
You could even #define some of the steps with nice gaps between:
#define INIT_STEP_CPU 1 #define INIT_STEP_TIMERS INIT_STEP_CPU + 10 #define INIT_STEP_SDARM INIT_STEP_TIMERS + 10
But maybe it's all wishful thinking
Well let's hope not. Going back to my original request, I can see how your patch can be fairly easily modified to do what I require - simply by adding a tag to each init call indicating what it refers to (usb, mmc, uart, etc.) and then providing a list of tags we want to init for.
Regards Simon
Regards,
Graeme
On Tuesday, August 16, 2011 23:25:35 Simon Glass wrote:
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
i'm not sure about this statement. many frameworks decouple the "register" step from the "initialize the hardware" step. i believe USB, SD/MMC, and Ethernet (ignoring the MAC address issue) do already.
arches calling i2c_init() in their arch/*/board.c are broken imo. only a few do it: arm, ppc, m68k. the common "i2c" command already takes care of exposing "i2c reset" for people to init this as necessary, and other arches havent had any troubles that i can see (certainly i know people have used i2c on Blackfin systems from u-boot).
a UART gets initialized all the time as it is the serial console ... not much to do here i dont think, and the overhead here tends to be fairly low as you program a few regs without polling for status updates.
LCDs should only get initialized if it's the splash screen, otherwise i cant think of any reason that hardware would ever get touched. so if you dont want the overhead of programming that hardware, then dont enable splash screen support ? i cant see a situation where you'd enable splash screen support but not actually show the splash screen ...
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
this is generally the policy now. init code should only be *registering* the availability of devices. it shouldnt be initializing the actual hardware until requested.
i know NAND flashes misbehave, and i posted a few patches to fix that, but there was one or two edge cases that needed addressing before it could be merged. -mike
Hi Mike,
On Thu, Aug 18, 2011 at 8:33 AM, Mike Frysinger vapier@gentoo.org wrote:
On Tuesday, August 16, 2011 23:25:35 Simon Glass wrote:
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
i'm not sure about this statement. many frameworks decouple the "register" step from the "initialize the hardware" step. i believe USB, SD/MMC, and Ethernet (ignoring the MAC address issue) do already.
Yes that is true in many cases.
As an example, I feel it is best that most/all the code to do with USB sits in the USB driver. Let's say we have usb_lowlevel_init() which sets up the SOC and then usb_start() which starts up a particular port. Then I don't want to call either of these until I decide that USB is required. The way board files tend to work today is to just have a list of calls to init routines, then rely on #ifdef to disable what is not required.
My desire is to make the decision on what to init at run-time rather than compile-time. The boot moves through specific stages where we need to bring in progressively more smarts to complete sucessfully. Initially we can just use eMMC, then we find that doesn't work so must use USB or later maybe network. But we don't want to execute the init code for all of that stuff up front - and in fact if you saw my postload email, the code may not even be loaded at that point.
As you suggest there is the option of doing the bare minimum init and then later when we do usb_start() we notice that we haven't called usb_lowlevel_init() yet. If we have a proper driver framework then we can keep track of which drivers have been activated, and activate USB before it is used.
arches calling i2c_init() in their arch/*/board.c are broken imo. only a few do it: arm, ppc, m68k. the common "i2c" command already takes care of exposing "i2c reset" for people to init this as necessary, and other arches havent had any troubles that i can see (certainly i know people have used i2c on Blackfin systems from u-boot).
I feel the idea of calling i2c_init() multiple times with a speed parameter is not great. Perhaps the function is just misnamed.
a UART gets initialized all the time as it is the serial console ... not much to do here i dont think, and the overhead here tends to be fairly low as you program a few regs without polling for status updates.
Yes.
LCDs should only get initialized if it's the splash screen, otherwise i cant think of any reason that hardware would ever get touched. so if you dont want the overhead of programming that hardware, then dont enable splash screen support ? i cant see a situation where you'd enable splash screen support but not actually show the splash screen ...
Well often U-Boot is asked to set up the LCD so that it will work for the kernel. There may be a specific power-on init sequence to follow even if nothing is actually written to the screen. For example in Chrome OS we don't have splash screen support but still init the LCD.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
this is generally the policy now. init code should only be *registering* the availability of devices. it shouldnt be initializing the actual hardware until requested.
OK then I vote for a framework which understands this and calls driver init once (in a lazy fashion when needed if you like).
i know NAND flashes misbehave, and i posted a few patches to fix that, but there was one or two edge cases that needed addressing before it could be merged. -mike
Regards, Simon
On Thursday, August 18, 2011 11:59:35 Simon Glass wrote:
On Thu, Aug 18, 2011 at 8:33 AM, Mike Frysinger wrote:
On Tuesday, August 16, 2011 23:25:35 Simon Glass wrote:
When U-Boot starts up it initializes all the peripherals which are enabled This might include USB, I2C, SD/MMC, LCD, Ethernet, UARTs, etc.
i'm not sure about this statement. many frameworks decouple the "register" step from the "initialize the hardware" step. i believe USB, SD/MMC, and Ethernet (ignoring the MAC address issue) do already.
Yes that is true in many cases.
As an example, I feel it is best that most/all the code to do with USB sits in the USB driver. Let's say we have usb_lowlevel_init() which sets up the SOC and then usb_start() which starts up a particular port. Then I don't want to call either of these until I decide that USB is required. The way board files tend to work today is to just have a list of calls to init routines, then rely on #ifdef to disable what is not required.
My desire is to make the decision on what to init at run-time rather than compile-time. The boot moves through specific stages where we need to bring in progressively more smarts to complete sucessfully. Initially we can just use eMMC, then we find that doesn't work so must use USB or later maybe network. But we don't want to execute the init code for all of that stuff up front - and in fact if you saw my postload email, the code may not even be loaded at that point.
i dont follow. before u-boot gets to command line processing (either the "bootcommand" env var or user input), little to no hardware should be initialized, only registered as available. after that, what hardware actually gets poked is completely user decided at run-time.
dont want to use usb hardware ? then dont call "usb start". dont want to use network hardware ? then dont do network commands (i.e. tftp).
what am i missing ?
arches calling i2c_init() in their arch/*/board.c are broken imo. only a few do it: arm, ppc, m68k. the common "i2c" command already takes care of exposing "i2c reset" for people to init this as necessary, and other arches havent had any troubles that i can see (certainly i know people have used i2c on Blackfin systems from u-boot).
I feel the idea of calling i2c_init() multiple times with a speed parameter is not great. Perhaps the function is just misnamed.
perhaps it is more historical, but that is the current API, and it is already called multiple times, so it's required to work. i dont think this has been a big deal so far for driver writers, but that doesnt mean it has to stay this way. but wrt your requirements, i dont think we need to dive down that rabbit hole ... just kill off the explicit call to i2c_init() in the arm board.c.
LCDs should only get initialized if it's the splash screen, otherwise i cant think of any reason that hardware would ever get touched. so if you dont want the overhead of programming that hardware, then dont enable splash screen support ? i cant see a situation where you'd enable splash screen support but not actually show the splash screen ...
Well often U-Boot is asked to set up the LCD so that it will work for the kernel. There may be a specific power-on init sequence to follow even if nothing is actually written to the screen. For example in Chrome OS we don't have splash screen support but still init the LCD.
ruh-roh. i think this is generally considered the wrong way to do things. the kernel drivers should be able to pick up the hardware and have it work regardless of what the (possibly brain dead) firmware that came before it did. relying on the hardware to be in a certain state. it's even better done in the kernel as there you can do the init asynchronously whereas in u-boot, everything is single threaded.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
this is generally the policy now. init code should only be *registering* the availability of devices. it shouldnt be initializing the actual hardware until requested.
OK then I vote for a framework which understands this and calls driver init once (in a lazy fashion when needed if you like).
each framework should already do that. if there's a specific one you think is missing, then you should highlight it.
if you're talking about overhauling/unifying the driver model rather than each one being open coded, that's a different thing. but i dont think your current requirements (as i understand them) necessitates such effort. -mike
Hi Mike,
On Thu, Aug 18, 2011 at 11:54 AM, Mike Frysinger vapier@gentoo.org wrote:
On Thursday, August 18, 2011 11:59:35 Simon Glass wrote:
[snip snip]
i dont follow. before u-boot gets to command line processing (either the "bootcommand" env var or user input), little to no hardware should be initialized, only registered as available. after that, what hardware actually gets poked is completely user decided at run-time.
dont want to use usb hardware ? then dont call "usb start". dont want to use network hardware ? then dont do network commands (i.e. tftp).
what am i missing ?
OK that's not how it is at the moment in some cases, but fair enough. We have been pushing Tegra in that directly as it happens, but certainly there is still a fair amount of mandatory init which should be moved into / called from drivers.
arches calling i2c_init() in their arch/*/board.c are broken imo. only a few do it: arm, ppc, m68k. the common "i2c" command already takes care of exposing "i2c reset" for people to init this as necessary, and other arches havent had any troubles that i can see (certainly i know people have used i2c on Blackfin systems from u-boot).
I feel the idea of calling i2c_init() multiple times with a speed parameter is not great. Perhaps the function is just misnamed.
perhaps it is more historical, but that is the current API, and it is already called multiple times, so it's required to work. i dont think this has been a big deal so far for driver writers, but that doesnt mean it has to stay this way. but wrt your requirements, i dont think we need to dive down that rabbit hole ... just kill off the explicit call to i2c_init() in the arm board.c.
Er ok, but I found one in stdio.c!
LCDs should only get initialized if it's the splash screen, otherwise i cant think of any reason that hardware would ever get touched. so if you dont want the overhead of programming that hardware, then dont enable splash screen support ? i cant see a situation where you'd enable splash screen support but not actually show the splash screen ...
Well often U-Boot is asked to set up the LCD so that it will work for the kernel. There may be a specific power-on init sequence to follow even if nothing is actually written to the screen. For example in Chrome OS we don't have splash screen support but still init the LCD.
ruh-roh. i think this is generally considered the wrong way to do things. the kernel drivers should be able to pick up the hardware and have it work regardless of what the (possibly brain dead) firmware that came before it did. relying on the hardware to be in a certain state. it's even better done in the kernel as there you can do the init asynchronously whereas in u-boot, everything is single threaded.
We can't have a sensible console in U-Boot without keyboard and LCD - for me the splash screen is a separate issue.
Yes the single-threaded problem does make it tricky. Am thinking about that problem now.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
this is generally the policy now. init code should only be *registering* the availability of devices. it shouldnt be initializing the actual hardware until requested.
OK then I vote for a framework which understands this and calls driver init once (in a lazy fashion when needed if you like).
each framework should already do that. if there's a specific one you think is missing, then you should highlight it.
if you're talking about overhauling/unifying the driver model rather than each one being open coded, that's a different thing. but i dont think your current requirements (as i understand them) necessitates such effort.
I suppose the ad-hoc nature of drivers means that people miss the 'generally accepted way' that things are supposed to be done.
Regards, Simon
-mike
On Thursday, August 18, 2011 15:01:28 Simon Glass wrote:
On Thu, Aug 18, 2011 at 11:54 AM, Mike Frysinger wrote:
On Thursday, August 18, 2011 11:59:35 Simon Glass wrote: i dont follow. before u-boot gets to command line processing (either the "bootcommand" env var or user input), little to no hardware should be initialized, only registered as available. after that, what hardware actually gets poked is completely user decided at run-time.
dont want to use usb hardware ? then dont call "usb start". dont want to use network hardware ? then dont do network commands (i.e. tftp).
what am i missing ?
OK that's not how it is at the moment in some cases, but fair enough. We have been pushing Tegra in that directly as it happens, but certainly there is still a fair amount of mandatory init which should be moved into / called from drivers.
if there's specific frameworks/arches that always init hardware, then in general that's a bug and we should treat it as such (the u-boot policy doc explicitly bans this). each framework (since they're all open coded in their own way) will need to be reviewed. but hopefully there shouldn't be many.
arches calling i2c_init() in their arch/*/board.c are broken imo. only a few do it: arm, ppc, m68k. the common "i2c" command already takes care of exposing "i2c reset" for people to init this as necessary, and other arches havent had any troubles that i can see (certainly i know people have used i2c on Blackfin systems from u-boot).
I feel the idea of calling i2c_init() multiple times with a speed parameter is not great. Perhaps the function is just misnamed.
perhaps it is more historical, but that is the current API, and it is already called multiple times, so it's required to work. i dont think this has been a big deal so far for driver writers, but that doesnt mean it has to stay this way. but wrt your requirements, i dont think we need to dive down that rabbit hole ... just kill off the explicit call to i2c_init() in the arm board.c.
Er ok, but I found one in stdio.c!
i'd also vote that as a bug :). in looking at the history, i think this is just a really old wart that we should burn off (it predates the git history which goes back to 2000-2002). if there are specific devices that need i2c, they themselves should be calling i2c_init().
i know Wolfgang is sometimes hesitant to change these long seated things, so we might have to do what i was doing with the nand change ... the default is kept for a while, but people get a build warning if they are implicitly opted into the old behavior. and if a board porter hasnt picked up their pieces by the time we drop the old behavior, well that's now their problem. most people (the active) ones will continue to work.
check out the commit here: http://git.denx.de/?p=u-boot/u-boot- blackfin.git;a=commit;h=df57f7de71fd1540991a0099be307a65679c53bb
LCDs should only get initialized if it's the splash screen, otherwise i cant think of any reason that hardware would ever get touched. so if you dont want the overhead of programming that hardware, then dont enable splash screen support ? i cant see a situation where you'd enable splash screen support but not actually show the splash screen ...
Well often U-Boot is asked to set up the LCD so that it will work for the kernel. There may be a specific power-on init sequence to follow even if nothing is actually written to the screen. For example in Chrome OS we don't have splash screen support but still init the LCD.
ruh-roh. i think this is generally considered the wrong way to do things. the kernel drivers should be able to pick up the hardware and have it work regardless of what the (possibly brain dead) firmware that came before it did. relying on the hardware to be in a certain state. it's even better done in the kernel as there you can do the init asynchronously whereas in u-boot, everything is single threaded.
We can't have a sensible console in U-Boot without keyboard and LCD - for me the splash screen is a separate issue.
Yes the single-threaded problem does make it tricky. Am thinking about that problem now.
if the hardware can be split up into the "prime the settings, wait for things to prime, and then do something else", you could (ab)use the current board callback system (where the board gets access to a few hooks along the way) to split up the LCD init so that the polling-some-registers part doesnt really happen.
if you wanted to talk about not touching the LCD at all *unless* someone wanted to interact with the keyboard, that might be an interesting discussion. we could add a hook to the shell interpreter where it would call a board func upon first user input. then you could skip the LCD part in the default (since you just want to boot linux automatically), but if someone wanted to interrupt that and talk to u-boot to debug, you'd get a slight pause. optimize for the common and make the uncommon [debug] step take a little longer.
To save time, reduce the amount of code executed and thereby improve security, we are wanting to initialize only some peripherals at the start. For example we might start up I2C and SC/MMC.
this is generally the policy now. init code should only be *registering* the availability of devices. it shouldnt be initializing the actual hardware until requested.
OK then I vote for a framework which understands this and calls driver init once (in a lazy fashion when needed if you like).
each framework should already do that. if there's a specific one you think is missing, then you should highlight it.
if you're talking about overhauling/unifying the driver model rather than each one being open coded, that's a different thing. but i dont think your current requirements (as i understand them) necessitates such effort.
I suppose the ad-hoc nature of drivers means that people miss the 'generally accepted way' that things are supposed to be done.
yes, but over the years i think (hope?) we've gotten better at catching this when someone submits something new. -mike
Hi Mike,
On Thu, Aug 18, 2011 at 1:53 PM, Mike Frysinger vapier@gentoo.org wrote:
On Thursday, August 18, 2011 15:01:28 Simon Glass wrote:
...
OK that's not how it is at the moment in some cases, but fair enough. We have been pushing Tegra in that directly as it happens, but certainly there is still a fair amount of mandatory init which should be moved into / called from drivers.
if there's specific frameworks/arches that always init hardware, then in general that's a bug and we should treat it as such (the u-boot policy doc explicitly bans this). each framework (since they're all open coded in their own way) will need to be reviewed. but hopefully there shouldn't be many.
OK
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Er ok, but I found one in stdio.c!
i'd also vote that as a bug :). in looking at the history, i think this is just a really old wart that we should burn off (it predates the git history which goes back to 2000-2002). if there are specific devices that need i2c, they themselves should be calling i2c_init().
i know Wolfgang is sometimes hesitant to change these long seated things, so we might have to do what i was doing with the nand change ... the default is kept for a while, but people get a build warning if they are implicitly opted into the old behavior. and if a board porter hasnt picked up their pieces by the time we drop the old behavior, well that's now their problem. most people (the active) ones will continue to work.
check out the commit here: http://git.denx.de/?p=u-boot/u-boot- blackfin.git;a=commit;h=df57f7de71fd1540991a0099be307a65679c53bb
OK I see.
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We can't have a sensible console in U-Boot without keyboard and LCD - for me the splash screen is a separate issue.
Yes the single-threaded problem does make it tricky. Am thinking about that problem now.
if the hardware can be split up into the "prime the settings, wait for things to prime, and then do something else", you could (ab)use the current board callback system (where the board gets access to a few hooks along the way) to split up the LCD init so that the polling-some-registers part doesnt really happen.
Yes - would like to hide all delays behind other running code, without firing up the second CPU. But LCD is the worst.
if you wanted to talk about not touching the LCD at all *unless* someone wanted to interact with the keyboard, that might be an interesting discussion. we could add a hook to the shell interpreter where it would call a board func upon first user input. then you could skip the LCD part in the default (since you just want to boot linux automatically), but if someone wanted to interrupt that and talk to u-boot to debug, you'd get a slight pause. optimize for the common and make the uncommon [debug] step take a little longer.
That's exactly the sort of thing that I think a driver framework would handle nicely, and generically.
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I suppose the ad-hoc nature of drivers means that people miss the 'generally accepted way' that things are supposed to be done.
yes, but over the years i think (hope?) we've gotten better at catching this when someone submits something new. -mike
Yes, the code is definitely improving so I think you are right.
Regards, Simon
participants (3)
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Graeme Russ -
Mike Frysinger -
Simon Glass