Re: [PATCH 0/2] gpiolib: Fix issues introduced by fast bitmap processing path

Hi Marek,

2018-09-24 11:43 GMT+02:00, Marek Szyprowski [off-list ref]:

Hi Janusz,

On 2018-09-24 01:53, Janusz Krzysztofik wrote:

quoted

While investigating possible reasons of GPIO fast bitmap processing
related boot hang on Samsung Snow Chromebook, reported by Marek
Szyprowski (thanks!), I've discovered one coding bug, addressed by
PATCH 1/2 of this series, and one potential regression introduced at
design level of the solution, hopefully fixed by PATCH 2/2.  See
commit messages for details.

Janusz Krzysztofik (2):
       gpiolib: Fix missing updates of bitmap index
       gpiolib: Fix array members of same chip processed separately

The fixes should resolve the boot hang observed by Marek, however the
second change excludes that particular case from fast bitmap processing
and restores the old behaviour.

I confirm, that the above 2 patches fixes boot issue on Samsung Snow
Chromebook with next-20180920.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

quoted

Hence, it is possible still another
issue which have had an influence on that boot hang exists in the code.
In order to fully verify the fix, it would have to be tested on a
platform where an array of GPIO descriptors is used which starts from
at least two consecutive pins of one GPIO chip in hardware order,
starting ftom 0, followed by one or more pins belonging to other
chip(s).

In order to verify if separate calls to .set() chip callback for each
pin instead of one call to .set_multiple() is actually the reason of
boot hang on Samsung Snow Chromebook, the affected driver -
drivers/mmc/core/pwrseq_simple.c - would have to be temporarily
modified for testing purposes so it calls gpiod_set_value() for each
pin instead of gpiod_set_array_value() for all of them.  If that would
also result in boot hang, we could be sure the issue was really the
one addressed by the second fix.  Marek, could you please try to
perform such test?

Yes, I've just tested next-20180920 only with the first patch from this
patchset and the mentioned change to drivers/mmc/core/pwrseq_simple.c.
It boots fine, so indeed the issue is in handling of arrays of gpios.

Just to be sure I did it right, this is my change to the mentioned file:

Yeah, that's what I had on mind.  However, I'd be more lucky if it didn't work
for you.  Setting the pins sequentially, not simultaneously as before, was
exactly what I hoped was the reason of the hang.

The only difference from the behaviour when the hang was occurring is now
the order the pins are manipulated.  Maybe that matters?
Could you please retry the same with the order of pins reversed, either in
the .dts file or here inside this for loop?

Thanks,
Janusz

+ gpiod_set_value_cansleep(reset_gpios->desc[i], value);
  }

  static void mmc_pwrseq_simple_pre_power_on(struct mmc_host *host)


Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland