linux-kernel - Re: [RFC] firmware load: defer request_firmware during early boot and resume

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Message-Id: <201207212333.05911.rjw@sisk.pl>
Date:	Sat, 21 Jul 2012 23:33:05 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-usb" <linux-usb@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Oliver Neukum <oneukum@...e.de>
Subject: Re: [RFC] firmware load: defer request_firmware during early boot and resume

On Saturday, July 21, 2012, Ming Lei wrote:
> On Sun, Jul 22, 2012 at 1:49 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Friday, July 20, 2012, Ming Lei wrote:
> 
> >> +     if (system_state != SYSTEM_RUNNING)
> >> +             return -EPROBE_DEFER;
> >
> > You can't just return here, _request_firmware_cleanup() has to be done still.
> 
> Good catch, thanks.
> 
> >
> >> +
> >>       ret = usermodehelper_read_trylock();
> >
> > So why don't you do this here, actually, like:
> >
> >         if (ret) {
> >                 ret = -EPROBE_DEFER;
> 
> The problem is that the 'ret' is zero for early boot situation.

If you don't use SYSTEM_SUSPEND, you could just leave your !SYSTEM_RUNNING
check above and use this one to cover the suspend/resume case.

However, this is all moot in the face of the Linus' objection.

> >         } else {
> >
> > instead of the WARN_ON()?
> >
> > Arguably, all cases in which usermodehelper_read_trylock() returns error
> > codes will require deferred probing.
> 
> Yes, looks !SYSTEM_RUNNING has covered all the cases already.

Well, not really.

> >
> >>       if (WARN_ON(ret)) {
> >>               dev_err(device, "firmware: %s will not be loaded\n", name);
> >> diff --git a/include/linux/device.h b/include/linux/device.h
> >> index d0e4d99..a63d3171 100644
> >> --- a/include/linux/device.h
> >> +++ b/include/linux/device.h
> >> @@ -244,7 +244,7 @@ extern struct device_driver *driver_find(const char *name,
> >>                                        struct bus_type *bus);
> >>  extern int driver_probe_done(void);
> >>  extern void wait_for_device_probe(void);
> >> -
> >> +extern void driver_deferred_probe_trigger(void);
> >>
> >>  /* sysfs interface for exporting driver attributes */
> >>
> >> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> >> index e07f5e0..c8d74c6 100644
> >> --- a/include/linux/kernel.h
> >> +++ b/include/linux/kernel.h
> >> @@ -378,6 +378,7 @@ extern enum system_states {
> >>       SYSTEM_POWER_OFF,
> >>       SYSTEM_RESTART,
> >>       SYSTEM_SUSPEND_DISK,
> >> +     SYSTEM_SUSPEND,
> >
> > First off, SYSTEM_SUSPEND_DISK is not used and probably should be removed.
> > Second, both SYSTEM_SUSPEND and SYSTEM_SUSPEND_DISK would require the same
> > kind of handling in the respect of device probing, so it is not sufficient
> > to change the state in suspend_devices_and_enter().
> 
> suspend_devices_and_enter is used by hibernation too,

No now look for the second time and then tell me what you got wrong.  OK?

> and the state is just updated to RUNNING after suspend_finish.

No, it is not.

> > Moreover, there are other situations in which tasks are frozen and
> > request_firmware() won't work just as well, so I don't think using
> > system_state for that is going to work in general.
> 
> Looks system_state becoming SYSTEM_RUNNING means all tasks has
> been thawed completely.

No, it doesn't.

Thanks,
Rafael
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