Requiring SPL_DM for new boards?
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
Regards, Simon
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
Regards, Simon
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
Hi Tom,
On Sun, 30 Oct 2022 at 11:53, Tom Rini trini@konsulko.com wrote:
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
OK:
$./tools/moveconfig.py -b
$ ./tools/moveconfig.py -f SPL ~SPL_DM 323 matches ...
$ ./tools/moveconfig.py -f SPL_DM 333 matches ...
Regards, Simon
On Mon, Oct 31, 2022 at 01:27:06PM -0600, Simon Glass wrote:
Hi Tom,
On Sun, 30 Oct 2022 at 11:53, Tom Rini trini@konsulko.com wrote:
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
OK:
$./tools/moveconfig.py -b
$ ./tools/moveconfig.py -f SPL ~SPL_DM 323 matches ...
$ ./tools/moveconfig.py -f SPL_DM 333 matches ...
OK, if we start parsing things out, PowerPC is one chunk of that and won't change. Another chunk of that is sunxi which is a "still making new SoCs with very small SRAM" and it's worth talking with Andre for thoughts there. A large swath of the rest is layerscape / imx6/7/8 and it's worth rfc'ing a patch or two to move their board-specific "select SPL_DM if SPL" to a higher level ARCH_xxx line. Especially for the imx8* ones.
On Mon, 31 Oct 2022 15:43:01 -0400 Tom Rini trini@konsulko.com wrote:
Hi Tom, Simon,
On Mon, Oct 31, 2022 at 01:27:06PM -0600, Simon Glass wrote:
Hi Tom,
On Sun, 30 Oct 2022 at 11:53, Tom Rini trini@konsulko.com wrote:
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
Hi,
What do people think about requiring SPL_DM for new boards? Would that cause any problems?
There is not much use of of-platdata (compiling the DT into C to save space) - is that because it doesn't work for people?
I am particularly keen to drop the old block interface from SPL. It seems to me that boards that can use that might have enough space to enable SPL_DM and SPL_DM_BLK? What do people think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
OK:
$./tools/moveconfig.py -b
$ ./tools/moveconfig.py -f SPL ~SPL_DM 323 matches ...
$ ./tools/moveconfig.py -f SPL_DM 333 matches ...
OK, if we start parsing things out, PowerPC is one chunk of that and won't change. Another chunk of that is sunxi which is a "still making new SoCs with very small SRAM" and it's worth talking with Andre for thoughts there.
Most newer SoCs are not that seriously limited anymore - though that's not universal, since Allwinner is still making a lot of new "small" SoCs (with single Cortex-A7s (or older!) and embedded DRAM). And regardless of that, until recently the BROM wouldn't load more than 32 KB into SRAM, anyway. So I cannot say for sure what the situation for new "boards" (rather SoCs?) will be, but we are stuck with the current legacy SPL for existing SoCs, for sure. Samuel has been working on SPL_DM for the D1 (RISC-V) port, though I am not a big fan of it: - We would still need the legacy SPL code, since older SoCs are still bound to the 32K limit. That is already a stretch for SoCs like the A64, where we are already very close to that limit. - It adds to the test matrix, since we now need to support and maintain DM/proper, legacy SPL and SPL-DM. - Forcing a DT and DM code into that very restricted space requires too many compromises for my taste. I like nice driver frameworks and love DT, but one must be able to afford all of this. If you have 100s of KBs or MBs available, that's all fine, but cutting corners to make it fit into 32K takes away much of the beauty and flexibility. The DT changes (u-boot,dm-pre-reloc) we need to make are some sign of it. - We actually don't gain much, because the information the SPL needs is mostly not in the DT to begin with: - The whole DT clock node is opaque, it basically just says "it's this SoC's CCU". That is OK for a single image kernel like Linux, but the SPL knows that already - either by build time config or by reading the SOCID register. And the SPL does *basic* clock setup, which we cannot really describe in the DT at all. - The situation is similar for pinctrl: the actual mux value for a certain function is not in the DT, but hardcoded in the driver. We already tried to hack this down for U-Boot, and only got away with quite some squinting. - The DRAM controller isn't even mentioned in the DT. And while we could add that, the information we need is very minimal. - For storage devices (MMC, SPI-NOR) we can use the same fixed per-SoC values as the BROM does, so just need the base address. There are only like four different values across all Allwinner SoCs. The rest of the DT node is either not useful (opaque clock handles) or not needed (interrupts).
Yes, there are some boards which require regulator setup in the SPL, which is described in the DT, but again this still requires regulator knowledge in the code, and is also quite universal (mostly by SoC again).
So in summary: it would be a lot of work, which we cannot extend to older SoCs because of technical limitations. But more importantly I think we don't gain much to make it worth.
Historically we more naturally shared code between SPL and U-Boot proper, because U-Boot proper used to look much like the SPL looks today (clock code, for instance). But much of this is mostly obsolete, because there is not much overlap, code-wise, the only exception being the common MMC protocol handling, maybe. So I am actually more tempted to spell this out more openly, and separate and trim down the SPL code, avoiding full-featured (DM) drivers at all, if possible (like the SPI NOR code does).
We can look into parsing the DT to gather base addresses (and putting them into generated headers), or to enable Kconfig options (board needs a regulator), but I would very much like to keep the SPL lean and mean.
The BROM is able to do all the loading without *any* board information whatsoever. All that the BROM is missing is the DRAM init, which requires just two or three parameters (LPDDR vs. DDR, frequency). So we could actually live with a *per-SoC* SPL: we know where the BROM booted from, so can continue doing so using the same fixed settings as the BROM used (for SD card, eMMC, SPI, FEL). We actually exercise this idea already in arch/arm/mach-sunxi/spl_spi_sunxi.c, which is separate from the normal SPI-NOR code, just focusing on some conservative read-only command to get the FIT image into DRAM. I would rather go into this direction than forcing DM into the SPL.
Cheers, Andre.
Hi all,
Thanks for CCing me, Andre.
On 11/1/22 13:15, Andre Przywara wrote:
On Mon, 31 Oct 2022 15:43:01 -0400 Tom Rini trini@konsulko.com wrote:
Hi Tom, Simon,
On Mon, Oct 31, 2022 at 01:27:06PM -0600, Simon Glass wrote:
Hi Tom,
On Sun, 30 Oct 2022 at 11:53, Tom Rini trini@konsulko.com wrote:
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote:
> Hi, > > What do people think about requiring SPL_DM for new boards? > Would that cause any problems? > > There is not much use of of-platdata (compiling the DT into C > to save space) - is that because it doesn't work for people?
Indeed, I tried enabling of-platdata on sunxi at one time, and it was not feasible to get working. Some of the issues I saw:
- There was no support for udevice_id::data -> udevice::driver_data. Several of our drivers share one U_BOOT_DRIVER for the entire SoC family; DM_DRIVER_ALIAS would need to plumb through a data argument.
- Functions like clk_get_by_index and gpio_request_by_name would need to work at least for index zero, where you could sort of get away with not being able to read #foo-cells from the supplier. (The OF_PLATDATA code would need to rewrite phandles to device IDs.) Otherwise, you need totally separate code for OF_PLATDATA vs OF_REAL.
- We recently converted our platform to use the pinctrl nodes from the devicetree (PINCTRL_GENERIC) in U-Boot proper. That does not work at all with OF_PLATDATA.
> I am particularly keen to drop the old block interface from > SPL. It seems to me that boards that can use that might have > enough space to enable SPL_DM and SPL_DM_BLK? What do people > think?
I don't think this works. The problem is we aren't seeing new SoCs that have a large initial amount of memory but rather many continuing to have 32KiB or similar tiny sizes. So, I'd rather continue to go with saying it's optional, but that we won't introduce new SPL functionality that can be DM or not DM, but only new functionality that needs SPL_DM and if platforms want it, but have limited memory, we need to go TPL->SPL in that case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
OK:
$./tools/moveconfig.py -b
$ ./tools/moveconfig.py -f SPL ~SPL_DM 323 matches ...
$ ./tools/moveconfig.py -f SPL_DM 333 matches ...
OK, if we start parsing things out, PowerPC is one chunk of that and won't change. Another chunk of that is sunxi which is a "still making new SoCs with very small SRAM" and it's worth talking with Andre for thoughts there.
Most newer SoCs are not that seriously limited anymore - though that's not universal, since Allwinner is still making a lot of new "small" SoCs (with single Cortex-A7s (or older!) and embedded DRAM). And regardless of that, until recently the BROM wouldn't load more than 32 KB into SRAM, anyway.
Starting with H6, and as far as I know for every SoC after that, the normal BROM will load up to the full size of SRAM A1 + SRAM C, which is
96 KB. That is plenty of space for SPL_DM + SPL_OF_REAL. I can look
back at my BROM analyses if you want the exact numbers.
So I don't think it is correct to say Allwinner is "still making new SoCs with very small SRAM".
So I cannot say for sure what the situation for new "boards" (rather SoCs?) will be, but we are stuck with the current legacy SPL for existing SoCs, for sure.
That is mostly true, with the exception that H6 and H616 can upgrade to SPL_DM. As you mention, A64 and H5 are the most problematic cases, since they are aarch64 but still have the 32 KB limit.
Samuel has been working on SPL_DM for the D1 (RISC-V) port, though I am not a big fan of it:
- We would still need the legacy SPL code, since older SoCs are still bound to the 32K limit. That is already a stretch for SoCs like the A64, where we are already very close to that limit.
- It adds to the test matrix, since we now need to support and maintain DM/proper, legacy SPL and SPL-DM.
I agree that there is some additional complication here, with the two main sources of surprising differences between the SPL and U-Boot DM execution environment being inconsistent Kconfig options and malloc.
However, on the driver side, the code running under SPL_DM and U-Boot is exactly the same. There is not a third driver variant.
- Forcing a DT and DM code into that very restricted space requires too many compromises for my taste. I like nice driver frameworks and love DT, but one must be able to afford all of this. If you have 100s of KBs or MBs available, that's all fine, but cutting corners to make it fit into 32K takes away much of the beauty and flexibility. The DT changes (u-boot,dm-pre-reloc) we need to make are some sign of it.
Yes, I would *really* appreciate the ability to skip fdtgrep and just put the whole devicetree in SPL, or at least have it be much more conservative about what it drops (certain properties, disabled nodes) so that annotating the devicetree is not necessary.
The current Makefile logic does not allow us to have a per-SoC "-u-boot.dtsi" file, so we would need to annotate per board. But even if it did, I don't want to pick and choose nodes; that's what Kconfig is for!
- We actually don't gain much, because the information the SPL needs is mostly not in the DT to begin with:
- The whole DT clock node is opaque, it basically just says "it's this SoC's CCU". That is OK for a single image kernel like Linux, but the SPL knows that already - either by build time config or by reading the SOCID register. And the SPL does *basic* clock setup, which we cannot really describe in the DT at all.
- The situation is similar for pinctrl: the actual mux value for a certain function is not in the DT, but hardcoded in the driver. We already tried to hack this down for U-Boot, and only got away with quite some squinting.
You say "we don't gain much", but I see clk_enable() and the automatic pinctrl_select_state() Just Working as an absolutely massive improvement.
Currently, SoC bringup requires updating the DT driver... and then 20+ ifdefs in various files. If new SoCs use SPL_DM, then new SoCs just need an updated DT driver. They don't have to touch any of the ifdefs.
- The DRAM controller isn't even mentioned in the DT. And while we could add that, the information we need is very minimal.
It is; the DRAM controller is the mbus node.
Writing a DM driver for the DRAM controller is effectively the same amount of effort as doing it the legacy way. You just wrap it in a U_BOOT_DRIVER and do the init in the .probe function. The change in the board code is similarly trivial:
- sunxi_dram_init(); + uclass_get_device(UCLASS_RAM, 0, &dev);
- For storage devices (MMC, SPI-NOR) we can use the same fixed per-SoC values as the BROM does, so just need the base address. There are only like four different values across all Allwinner SoCs. The rest of the
There are even fewer values to keep track of if the only MMIO addresses hardcoded in some header are the ones for pre-H6 SoCs ;-).
DT node is either not useful (opaque clock handles) or not needed (interrupts).
As long as you ignore raw NAND, maybe you can get away with using slow, safe code like the BROM does. But sometimes you really do need per-board information like ECC parameters from the DT node.
Yes, there are some boards which require regulator setup in the SPL, which is described in the DT, but again this still requires regulator knowledge in the code, and is also quite universal (mostly by SoC again).
So in summary: it would be a lot of work, which we cannot extend to older SoCs because of technical limitations. But more importantly I think we don't gain much to make it worth.
I agree that old SoCs pre-H6 are stuck for now. But I do see a lot of benefit for new SoCs. Especially when starting from a blank slate on RISC-V, it was much easier porting one set of drivers and SPL_DM, than porting two sets of drivers.
Historically we more naturally shared code between SPL and U-Boot proper, because U-Boot proper used to look much like the SPL looks today (clock code, for instance). But much of this is mostly obsolete, because there is not much overlap, code-wise, the only exception being the common MMC protocol handling, maybe. So I am actually more tempted to spell this out more openly, and separate and trim down the SPL code, avoiding full-featured (DM) drivers at all, if possible (like the SPI NOR code does).
We can look into parsing the DT to gather base addresses (and putting them into generated headers), or to enable Kconfig options (board needs a regulator), but I would very much like to keep the SPL lean and mean.
The BROM is able to do all the loading without *any* board information whatsoever. All that the BROM is missing is the DRAM init, which requires just two or three parameters (LPDDR vs. DDR, frequency). So we could actually live with a *per-SoC* SPL: we know where the BROM booted from, so can continue doing so using the same fixed settings as the BROM used (for SD card, eMMC, SPI, FEL). We actually exercise this idea already in arch/arm/mach-sunxi/spl_spi_sunxi.c, which is separate from the normal SPI-NOR code, just focusing on some conservative read-only command to get the FIT image into DRAM. I would rather go into this direction than forcing DM into the SPL.
I suppose there are two ways of thinking about SPL: 1) Exactly like U-Boot proper, except we removed all of the interactive parts to make it smaller. 2) Load U-Boot from a fixed location on disk as fast as possible using as little code as possible, and do nothing else.
The second view ignores things like disk/MTD partitions, verified boot, falcon mode, reboot modes, multi-DTB FITs, etc. that would benefit from having all of the DM and FDT infrastructure available. But on the other hand, it gets you a highly-optimized program that does one thing and does it well. I do like the idea of only needing one binary per SoC.
I guess my question is, what do the U-Boot maintainers want U-Boot SPL to be? If it's more like the first description, then maybe it makes more sense to build the lean and mean SPL outside the U-Boot infrastructure. Then if the SPL_DM migration is forced at some point, we could just disable SUPPORT_SPL for anything older than H6, and treat SPL as a blob. But that still seems like quite a lot of unnecessary work when we have a working U-Boot SPL for those SoCs today. What do you think?
Regards, Samuel
Hi,
On Tue, 1 Nov 2022 at 19:54, Samuel Holland samuel@sholland.org wrote:
Hi all,
Thanks for CCing me, Andre.
On 11/1/22 13:15, Andre Przywara wrote:
On Mon, 31 Oct 2022 15:43:01 -0400 Tom Rini trini@konsulko.com wrote:
Hi Tom, Simon,
On Mon, Oct 31, 2022 at 01:27:06PM -0600, Simon Glass wrote:
Hi Tom,
On Sun, 30 Oct 2022 at 11:53, Tom Rini trini@konsulko.com wrote:
On Sat, Oct 29, 2022 at 07:44:01PM -0600, Simon Glass wrote:
Hi Tom,
On Fri, 21 Oct 2022 at 10:26, Tom Rini trini@konsulko.com wrote:
> > On Fri, Oct 14, 2022 at 09:56:44AM -0600, Simon Glass wrote: > >> Hi, >> >> What do people think about requiring SPL_DM for new boards? >> Would that cause any problems? >> >> There is not much use of of-platdata (compiling the DT into C >> to save space) - is that because it doesn't work for people?
Indeed, I tried enabling of-platdata on sunxi at one time, and it was not feasible to get working. Some of the issues I saw:
- There was no support for udevice_id::data -> udevice::driver_data. Several of our drivers share one U_BOOT_DRIVER for the entire SoC family; DM_DRIVER_ALIAS would need to plumb through a data argument.
We could add that if you like.
- Functions like clk_get_by_index and gpio_request_by_name would need to work at least for index zero, where you could sort of get away with not being able to read #foo-cells from the supplier. (The OF_PLATDATA code would need to rewrite phandles to device IDs.) Otherwise, you need totally separate code for OF_PLATDATA vs OF_REAL.
Can you use clk_get_by_phandle() ?
- We recently converted our platform to use the pinctrl nodes from the devicetree (PINCTRL_GENERIC) in U-Boot proper. That does not work at all with OF_PLATDATA.
Right, and that is a pain. The use of strings and the big pinmux tables makes it quite a challenge.
Can you hard-code pinctrl for TPL, perhaps, then use the full driver in SPL?
>> I am particularly keen to drop the old block interface from >> SPL. It seems to me that boards that can use that might have >> enough space to enable SPL_DM and SPL_DM_BLK? What do people >> think? > > I don't think this works. The problem is we aren't seeing new > SoCs that have a large initial amount of memory but rather many > continuing to have 32KiB or similar tiny sizes. So, I'd rather > continue to go with saying it's optional, but that we won't > introduce new SPL functionality that can be DM or not DM, but > only new functionality that needs SPL_DM and if platforms want > it, but have limited memory, we need to go TPL->SPL in that > case.
OK I see.
What do you think of a migration method for boards which don't use SPL_DM, so they migrate to TPL? Would that cause a lot of problems?
I'm not sure what it gains us. Maybe the first step here is to see what the list of non-DM_SPL platforms / SoCs are?
OK:
$./tools/moveconfig.py -b
$ ./tools/moveconfig.py -f SPL ~SPL_DM 323 matches ...
$ ./tools/moveconfig.py -f SPL_DM 333 matches ...
OK, if we start parsing things out, PowerPC is one chunk of that and won't change. Another chunk of that is sunxi which is a "still making new SoCs with very small SRAM" and it's worth talking with Andre for thoughts there.
Most newer SoCs are not that seriously limited anymore - though that's not universal, since Allwinner is still making a lot of new "small" SoCs (with single Cortex-A7s (or older!) and embedded DRAM). And regardless of that, until recently the BROM wouldn't load more than 32 KB into SRAM, anyway.
Starting with H6, and as far as I know for every SoC after that, the normal BROM will load up to the full size of SRAM A1 + SRAM C, which is
96 KB. That is plenty of space for SPL_DM + SPL_OF_REAL. I can look
back at my BROM analyses if you want the exact numbers.
So I don't think it is correct to say Allwinner is "still making new SoCs with very small SRAM".
So I cannot say for sure what the situation for new "boards" (rather SoCs?) will be, but we are stuck with the current legacy SPL for existing SoCs, for sure.
That is mostly true, with the exception that H6 and H616 can upgrade to SPL_DM. As you mention, A64 and H5 are the most problematic cases, since they are aarch64 but still have the 32 KB limit.
Samuel has been working on SPL_DM for the D1 (RISC-V) port, though I am not a big fan of it:
- We would still need the legacy SPL code, since older SoCs are still bound to the 32K limit. That is already a stretch for SoCs like the A64, where we are already very close to that limit.
- It adds to the test matrix, since we now need to support and maintain DM/proper, legacy SPL and SPL-DM.
I agree that there is some additional complication here, with the two main sources of surprising differences between the SPL and U-Boot DM execution environment being inconsistent Kconfig options and malloc.
However, on the driver side, the code running under SPL_DM and U-Boot is exactly the same. There is not a third driver variant.
- Forcing a DT and DM code into that very restricted space requires too many compromises for my taste. I like nice driver frameworks and love DT, but one must be able to afford all of this. If you have 100s of KBs or MBs available, that's all fine, but cutting corners to make it fit into 32K takes away much of the beauty and flexibility. The DT changes (u-boot,dm-pre-reloc) we need to make are some sign of it.
Yes, I would *really* appreciate the ability to skip fdtgrep and just put the whole devicetree in SPL, or at least have it be much more conservative about what it drops (certain properties, disabled nodes) so that annotating the devicetree is not necessary.
The current Makefile logic does not allow us to have a per-SoC "-u-boot.dtsi" file, so we would need to annotate per board. But even if it did, I don't want to pick and choose nodes; that's what Kconfig is for!
- We actually don't gain much, because the information the SPL needs is mostly not in the DT to begin with:
- The whole DT clock node is opaque, it basically just says "it's this SoC's CCU". That is OK for a single image kernel like Linux, but the SPL knows that already - either by build time config or by reading the SOCID register. And the SPL does *basic* clock setup, which we cannot really describe in the DT at all.
- The situation is similar for pinctrl: the actual mux value for a certain function is not in the DT, but hardcoded in the driver. We already tried to hack this down for U-Boot, and only got away with quite some squinting.
You say "we don't gain much", but I see clk_enable() and the automatic pinctrl_select_state() Just Working as an absolutely massive improvement.
Currently, SoC bringup requires updating the DT driver... and then 20+ ifdefs in various files. If new SoCs use SPL_DM, then new SoCs just need an updated DT driver. They don't have to touch any of the ifdefs.
- The DRAM controller isn't even mentioned in the DT. And while we could add that, the information we need is very minimal.
It is; the DRAM controller is the mbus node.
Writing a DM driver for the DRAM controller is effectively the same amount of effort as doing it the legacy way. You just wrap it in a U_BOOT_DRIVER and do the init in the .probe function. The change in the board code is similarly trivial:
sunxi_dram_init();
uclass_get_device(UCLASS_RAM, 0, &dev);
- For storage devices (MMC, SPI-NOR) we can use the same fixed per-SoC values as the BROM does, so just need the base address. There are only like four different values across all Allwinner SoCs. The rest of the
There are even fewer values to keep track of if the only MMIO addresses hardcoded in some header are the ones for pre-H6 SoCs ;-).
DT node is either not useful (opaque clock handles) or not needed (interrupts).As long as you ignore raw NAND, maybe you can get away with using slow, safe code like the BROM does. But sometimes you really do need per-board information like ECC parameters from the DT node.
Yes, there are some boards which require regulator setup in the SPL, which is described in the DT, but again this still requires regulator knowledge in the code, and is also quite universal (mostly by SoC again).
So in summary: it would be a lot of work, which we cannot extend to older SoCs because of technical limitations. But more importantly I think we don't gain much to make it worth.
I agree that old SoCs pre-H6 are stuck for now. But I do see a lot of benefit for new SoCs. Especially when starting from a blank slate on RISC-V, it was much easier porting one set of drivers and SPL_DM, than porting two sets of drivers.
Historically we more naturally shared code between SPL and U-Boot proper, because U-Boot proper used to look much like the SPL looks today (clock code, for instance). But much of this is mostly obsolete, because there is not much overlap, code-wise, the only exception being the common MMC protocol handling, maybe. So I am actually more tempted to spell this out more openly, and separate and trim down the SPL code, avoiding full-featured (DM) drivers at all, if possible (like the SPI NOR code does).
We can look into parsing the DT to gather base addresses (and putting them into generated headers), or to enable Kconfig options (board needs a regulator), but I would very much like to keep the SPL lean and mean.
The BROM is able to do all the loading without *any* board information whatsoever. All that the BROM is missing is the DRAM init, which requires just two or three parameters (LPDDR vs. DDR, frequency). So we could actually live with a *per-SoC* SPL: we know where the BROM booted from, so can continue doing so using the same fixed settings as the BROM used (for SD card, eMMC, SPI, FEL). We actually exercise this idea already in arch/arm/mach-sunxi/spl_spi_sunxi.c, which is separate from the normal SPI-NOR code, just focusing on some conservative read-only command to get the FIT image into DRAM. I would rather go into this direction than forcing DM into the SPL.
I suppose there are two ways of thinking about SPL:
- Exactly like U-Boot proper, except we removed all of the interactive parts to make it smaller.
- Load U-Boot from a fixed location on disk as fast as possible using as little code as possible, and do nothing else.
The second view ignores things like disk/MTD partitions, verified boot, falcon mode, reboot modes, multi-DTB FITs, etc. that would benefit from having all of the DM and FDT infrastructure available. But on the other hand, it gets you a highly-optimized program that does one thing and does it well. I do like the idea of only needing one binary per SoC.
I guess my question is, what do the U-Boot maintainers want U-Boot SPL to be? If it's more like the first description, then maybe it makes more sense to build the lean and mean SPL outside the U-Boot infrastructure. Then if the SPL_DM migration is forced at some point, we could just disable SUPPORT_SPL for anything older than H6, and treat SPL as a blob. But that still seems like quite a lot of unnecessary work when we have a working U-Boot SPL for those SoCs today. What do you think?
I don't think of SPL as minimal anymore. It needs to load U-Boot, sometimes from a block device / filesystem. It probably uses FIT and may even load things like OP-TEE.
Should TPL be where SoCs do their very early non-DM init, if needed?
As I mentioned earlier, my goal is to require SPL_BLK if block devices are needed in SPL. Perhaps this might be possible for newer SoCs?
Regards, Simon
participants (4)
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Andre Przywara -
Samuel Holland -
Simon Glass -
Tom Rini