Dear =?UTF-8?q?Andreas=20Bie=C3=9Fmann?=,

In message 1291099039-49672-4-git-send-email-andreas.devel@googlemail.com you wrote:

Without this patch the linker will SEGFAULT on some undefined weak symbols.

Suggested-by: Sebastien Carlier sebastien.carlier@gmail.com Signed-off-by: Andreas Bießmann andreas.devel@googlemail.com

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arch/arm/cpu/arm920t/u-boot.lds | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-)

Applied, thanks.

Best regards,

Wolfgang Denk

Le 09/12/2010 08:24, Andreas Bießmann a écrit :

Dear Wolfgang Denk,

Am 08.12.2010 um 23:52 schrieb Wolfgang Denk:

...

Dear =?UTF-8?q?Andreas=20Bie=C3=9Fmann?=,

In message1291099039-49672-4-git-send-email-andreas.devel@googlemail.com you wrote:

...

Without this patch the linker will SEGFAULT on some undefined weak symbols.

Suggested-by: Sebastien Carliersebastien.carlier@gmail.com Signed-off-by: Andreas Bießmannandreas.devel@googlemail.com

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arch/arm/cpu/arm920t/u-boot.lds | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-)

Applied, thanks.

Please do not apply that patch! I'm sorry I have split up the thread cause it lead to a generic timer discussion. Therefore I posted v2 of this patch series here: http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/89974

This patch is not needed, if no undefined weak symbol is available. This patch adds .plt/.rel.plt section which has R_ARM_JUMP_SLOT which is not handled in code. Therefore we do not really know what this patch does to the code, it was mostly a patch to handle the linker segfault described several times.

Thanks for pointing this out. My bad: I did not relate the two series when going through patchwork.

Wolfgang, I was about to send out a revert but after pulling u-boot.git and u-boot-arm.git I don't see Andreas' patch in there. If you haven't committed it yet, maybe you can fix this yourself?

regards

Andreas Bießmann

Amicalement,

Dear Wolfgang Denk,

In message 20101209094538.7B9BBD08A93@gemini.denx.de you wrote:

Hm... strange...

I am absolutely sure that I did apply these patches last night, and then I even pushed them out... ... but now I see no trace of this either.

Don't know what happened (I should learn this lesson - this is what I get when _not_ having a beer ;-)

Ummm... now I have a problem, because I have marked all these patches as "applied", both in patchwork and in my mail reader. This actually means that I have completely lost track of what is missing and which patches should be applied :-(

OK, I found the stuff. I have applied to my working copy of the master branch instesd of ARM.

So only the "-pie" commit needs to be removed?

Best regards,

Wolfgang Denk

Dear Reinhard Meyer,

Am 30.11.2010 08:17, schrieb Reinhard Meyer:

Dear Andreas Bießmann,

...

Reuse the gd->tbl/tbu values for timestamp/lastinc bss values in arm920t/at91/timer driver.

I see your dilemma here.

tbu/tbl were introduced by me to form a true 64 bit monotonous incrementing value (like on most powerPC). You use tbl as the last (16 bit) value of the 16 bit hardware timer and tbu as the actual, only 32 bits worth time value. If the rest of the timer functions handle this correctly (I doubt that, but I cannot look at that right now), that "abuse" might be OK. But I rather have a field, say "u32 last_hw_val" (or a better name) added to the GD inside the AT91FAMILY define and have tbu/tbl really be a functional 64 bit value.

[snip]

I think get your point.

To get this bss issue fixed for v2010.12 I'd like to add another value to GD to hold the last hw timer value. My current usage of tbu should therefore go to tbl, to have a virutal 64 bit value just counting 32 bit, is that right?

Later on I also see some work in that arm920t/at91 SoC 'driver' section. E.g. we really do need something like arm926ejs/at91/clock to have the usart driver merged. And I might have some other changes to the timer part of arm920t/at91. I found out the at91rm9200 do also have a PIT ... but that is for later discussion.

regards

Andreas Bießmann

Dear Wolfgang Denk,

Am 30.11.2010 09:16, schrieb Wolfgang Denk:

Dear "=?UTF-8?B?QW5kcmVhcyBCaWXDn21hbm4=?=",

In message 4CF4AFED.1010609@gmail.com you wrote:

...

To get this bss issue fixed for v2010.12 I'd like to add another value to GD to hold the last hw timer value. My current usage of tbu should therefore go to tbl, to have a virutal 64 bit value just counting 32 bit, is that right?

That sounds like a terrible mess to me, please do not do that. Either we have a 64 bit counter, hen it should cound the full 64 bit range. Or use a plain uint32_t if 32 bit are sfficient. Don't play any tricks like misusing an "unused" part of one variable for other, independent purposes.

If I got Reinhard correct the uint32 values tbl and tbu do build the Upper and Lower part of an virtual 64 bit counter. His statement is to not use these values in another context like I did (32 bit timestamp and 32 bit 'lastinc' which is really 16 bit). Therefore I additionally suggested to have the idea with virtual 64 bit reproduced for at91rm9200 and use the lower part for timestamp.

I think we should provide a "uint64_t timebase" which represents a real 64 bit counter. And if you need a separate "uint32_t timelast" to store the previous timer value then please make this a separate variable.

As you suggested in another thread those changes will go into next branch. So for v2010.12 I'd like to have a 'short time' solution to get the at91rm9200 boards working. Is it OK to use the tbu/tbl values as mentioned above and then migrate to a uint64_t timebase later on?

regards

Andreas Bießmann

On 11/30/2010 1:14 AM, Reinhard Meyer wrote:

Dear Wolfgang Denk,

what we really need is only a 32 bit monotonous free running tick that increments at a rate of at least 1 MHz. As someone pointed out a while ago, even at 1GHz that would last for four seconds before it rolls over. But a 1HGz counter could be 64 bit internally and always be returned as 32 bits when it is shifted right to bring it into the "few" MHz range.

Any architecture should be able to provide such a 32 bit value. On powerpc that would simply be tbu|tbl shifted right a few bits.

An architecture and SoC specific timer should export 3 functions:

int timer_init(void); u32 get_tick(void); /* return the current value of the internal free running counter */ u32 get_tbclk(void); /* return the rate at which that counter increments (per second) */

A generic timer function common to *most* architectures and SoCs would use those two functions to provice udelay() and reset_timer() and get_timer(). Any other timer functions should not be required in u-boot anymore.

However get_timer() and reset_timer() are a bit of a functional problem:

currently reset_timer() does either actually RESET the free running timer (BAD!) or remember its current value in another (gd-)static variable which later is subtracted when get_timer() is called. That precludes the use of several timers concurrently.

Also, since the 1000Hz base for that timer is usually derived from get_tick() by dividing it by some value, the resulting 1000Hz base is not exhausting the 32 bits before it wraps to zero.

Therefore I propose two new functions that are to replace reset_timer() and get_timer():

u32 init_timeout(u32 timeout_in_ms); /* return the 32 bit tick value when the timeout will be */ bool is_timeout(u32 reference); /* return true if reference is in the past */

A timeout loop would therefore be like:

u32 t_ref = timeout_init(3000); /* init a 3 second timeout */

do ... loop ... while (!is_timeout(t_ref));

coarse sketches of those functions:

u32 init_timeout(u32 ms) { return get_ticks() + ((u64)get_tbclk() * (u64)ms) / (u64)1000; }

bool is_timeout(u32 reference) { return ((int)get_ticks() - (int)reference)> 0; }

Unfortunately this requires to "fix" all uses of get_timer() and friends, but I see no other long term solution to the current incoherencies.

Comments welcome (and I would provide patches)...

Hi All, The idea of changing the get_timer interface to the init_timeout/is_timeout pair has the advantage that it is only necessary to change the delay time in ms to an internal timebase once, and after that, only a 32-bit subtraction is required. I do not however like the idea of using 64 bit math to do so, as on many systems this is quite expensive. However, this is a feature that can be optimized for particular CPUs. I also REALLY don't like the idea of having a get_ticks function, because for sure people will use this instead of the desired interface to the timer because it is "better". Then we get back into a mess. Since in most cases get_ticks is one or two instructions, please, let us hide them in init_timeout/is_timeout. An alternate approach, which has the merit of being more like the originally intended interface, simply disallows reset_timer since it is totally unnecessary. The only dis-advantage of the original approach using just get_timer is that the conversion to ms must be considered at each call to get_timer, and will require at a minimum one 32 bit integer to remember the hardware timer value the last time get_timer was called (unless the hardware time can be trivially converted to a 32 bit value in ms, which is quite uncommon). This is not a high price to pay, and matches the current usage. This is probably for Mr. Denk to decide. If we were just starting now, the init_timeout/is_timeout is simpler, but since we are not, perhaps keeping the current approach has value. I would really like to help by providing some patches, but I am just way too busy at present.

Best Regards, Bill Campbell

Reinhard

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U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot

On 11/30/2010 7:48 AM, Reinhard Meyer wrote:

Dear J. William Campbell,

...

On 11/30/2010 1:14 AM, Reinhard Meyer wrote:

...

Dear Wolfgang Denk,

what we really need is only a 32 bit monotonous free running tick that increments at a rate of at least 1 MHz. As someone pointed out a while ago, even at 1GHz that would last for four seconds before it rolls over. But a 1HGz counter could be 64 bit internally and always be returned as 32 bits when it is shifted right to bring it into the "few" MHz range.

Any architecture should be able to provide such a 32 bit value. On powerpc that would simply be tbu|tbl shifted right a few bits.

An architecture and SoC specific timer should export 3 functions:

int timer_init(void); u32 get_tick(void); /* return the current value of the internal free running counter */ u32 get_tbclk(void); /* return the rate at which that counter increments (per second) */

A generic timer function common to *most* architectures and SoCs would use those two functions to provice udelay() and reset_timer() and get_timer(). Any other timer functions should not be required in u-boot anymore.

However get_timer() and reset_timer() are a bit of a functional problem:

currently reset_timer() does either actually RESET the free running timer (BAD!) or remember its current value in another (gd-)static variable which later is subtracted when get_timer() is called. That precludes the use of several timers concurrently.

Also, since the 1000Hz base for that timer is usually derived from get_tick() by dividing it by some value, the resulting 1000Hz base is not exhausting the 32 bits before it wraps to zero.

(###)

Hi All, A correct method to provide a full 32 bits of resolution at a 1 ms rate is simple. It requires maintaining a software timer in ms. This timer is updated by converting the difference in the hardware time base to ms and then adding the correct number of ms to the software timer. As previously discussed, this only requires calling get_timer once a second or so. The conversion can be made simply in most cases, especially if the clock rate is a "nice" number. Even in the worst case, it is not too hard to "adjust" the saved hardware timer value to contain any remainder ticks. Yes, if this is done incorrectly, the results are bad.

...

...

Therefore I propose two new functions that are to replace reset_timer() and get_timer():

u32 init_timeout(u32 timeout_in_ms); /* return the 32 bit tick value when the timeout will be */ bool is_timeout(u32 reference); /* return true if reference is in the past */

A timeout loop would therefore be like:

u32 t_ref = timeout_init(3000); /* init a 3 second timeout */

do ... loop ... while (!is_timeout(t_ref));

coarse sketches of those functions:

u32 init_timeout(u32 ms) { return get_ticks() + ((u64)get_tbclk() * (u64)ms) / (u64)1000; }

bool is_timeout(u32 reference) { return ((int)get_ticks() - (int)reference)> 0; }

Unfortunately this requires to "fix" all uses of get_timer() and friends, but I see no other long term solution to the current incoherencies.

Comments welcome (and I would provide patches)...

Hi All, The idea of changing the get_timer interface to the init_timeout/is_timeout pair has the advantage that it is only necessary to change the delay time in ms to an internal timebase once, and after that, only a 32-bit subtraction is required.

Exactly.

...

I do not however like the idea of using 64 bit math to do so, as on many systems this is quite expensive. However, this is a feature that can be optimized for particular CPUs.

64 Bit math is only necessary when get_tbclk() times the maximun anticipated timeout (in ms) is larger than 32 bits. This happens easyly when tbclk is a few MHz.

What I think you mean to say here is that the delay time fits easily into 32 bits for all reasonable clock rates. For instance, a 1 GHz clock rate yields a maximum delay of about 2 seconds in a 32 bit word? For fast clock rates, it is probably advisable to shift the 64 bit counter right a few bits to ensure adequate range.

Besides the current working(!) implementations use 64 bit math already.

In ARM perhaps, but I think there are lots of working 32 bit in other processors(?).

You can optimize into 32 bits by factoring the timeout_in_ms into whole seconds, and the remainder.

True.

...

I also REALLY don't like the idea of having a get_ticks function, because for sure people will use this instead of the desired interface to the timer because it is "better". Then we get back into a mess. Since in most cases get_ticks is one or two instructions, please, let us hide them in init_timeout/is_timeout.

Agreed. However I intended to split the timer into two sources (read above): one hardware dependant part exporting exactly those functions, and one generic part using them.

Yes, and that is EXACTLY what I think is a bad idea for the reason I mentioned. If the get_ticks interface is public, it will be used, and this will lead to problems (as it already has). Yes, we can say "don't do that", but people will do it anyway, and eventually it will sneak into the code base. Since the conversion to/from hardware resolution to 1 ms resolution becomes CPU dependent if any optimization is used, this operation really needs to be a per CPU thing.

...

    An alternate approach, which has the merit of being more like the

originally intended interface, simply disallows reset_timer since it is totally unnecessary. The only dis-advantage of the original approach using just get_timer is that the conversion to ms must be considered at each call to get_timer, and will require at a minimum one 32 bit integer to remember the hardware timer value the last time get_timer was called

"remembering" that inside the timer function is exactly what I want to get rid of. And that would not work in case of the usage method (2.) below.

...

(unless the hardware time can be trivially converted to a 32 bit value in ms, which is quite uncommon).

Indeed.

...

This is not a high price to pay, and matches the current usage. This is probably for Mr. Denk to decide. If

The "current usages" are mainly those two:

1. reset_timer(); ... if (get_timer(0)> TIMEOUT) ...

--> this is an ab-use, of course, but can be found in u-boot.

Getting rid of reset_reset timer detects all such abuses.

2. epoch = get_timer(0); ... if (get_timer(epoch)> TIMEOUT) ...

--> this is the correct way to use get_timer(), however it has the problem of incorrect rollover after 32 bits. See (###) above!

I assume by ### you mean that is get_timer(int x) is not based on a correct conversion of hardware time to a 1 ms timebase, there is a problem. 32 bits at 1 ms resolution is 49.7/2 days, so you can't mean this is the problem.

...

we were just starting now, the init_timeout/is_timeout is simpler, but since we are not, perhaps keeping the current approach has value.

Finding the current uses of get_timer() is a simple grep, fixing the code should not require more than a few minutes per location. Testing, however is a problem. But ANY change would require testing.

...

    I would really like to help by providing some patches, but I am

just way too busy at present.

Same here. Nevertheless some xmax holidays are coming up, and maybe some idle hours in them ;)

I hope so!

Best Regards, Bill Campbell

Best Regards, Reinhard