Hello,
On 2015-06-03 17:03, Guenter Roeck wrote:
On 06/03/2015 03:01 AM, Marek Szyprowski wrote:
Hello,
On 2015-06-02 17:29, Heiko Stübner wrote:
I'm confused by the pwrseq-emmc registering a restart_handler for
resetting an
emmc in a panic-reboot case at priority 129 to "schedules it just
before
system reboot".
>From what I remember from the restart-handler discussion the
actuall usage is
traversing the ordered list until one registered handler sucessfully
restarts
the system and not to have arbitary actions in there not related to
the actual
restart process?
The actual documentation in kernel/reboot.c supports this assumption,
describing register_restart_handler as "Register function to be
called to
reset the system".
Additionally, 128 isn't even _the_ priority to reboot the system as
described
above and some drivers use higher priorities per default, see in
drivers/power/reset arm-versatile-reboot.c; at91-reset.c;
rmobile-reset.c and
some more.
So I guess this should use some other mechanism (reboot notifier)
instead of
restart_handlers?
The first problem with reboot notifiers is that they are called too
early - before
device_shutdown(), what interferes with the code in mmc_bus_shutdown
and causes
lockup. The second problem is
that reboot notifiers are not called from emergency_restart() path. I
agree that
129 value for priority might not be the best, maybe according to
documentation,
255 value should be used to ensure that the handler will be called
first before
any real restart handler.
There is no non-real restart handler, and the documentation does not
say anything
about "called first before any real restart handler". Even with a
priority of 255
you would have no guarantee that your handler is called. Restart
handlers are
supposed to restart the system, nothing else. Actually, you have no
guarantee
that the restart handler is called in the first place - not all
architectures
support it (currently only arm, arm64, and mips do). Presumably mmc
support is
not limited to those architectures.
If you have any idea how to avoid restart handler and ensure proper
eMMC card
reboot sequence on any system reboot, I'm open for suggestions.
Why not execute the device-specific restart in the shutdown function ?
You could register a reboot notifier to mark that a reboot is happening,
and then execute the restart at the end of mmc_bus_shutdown.
Okay, this will solve one issue with reboot notifier, but there is still
a problem
with emergency_restart(). Do you think that it will be okay to add a call to
restart_notifiers (for example with some higher priority) also for
emergency case?
If so, I can rework my emmc pwr seq driver to use it and propose a patch for
emergency restart code.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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