Re: [PATCH] leds:lp55xx: Correct Kconfig dependency for f/w user helper

[Takashi Iwai <tiwai@suse.de>]

On Tue, 08 Sep 2015 02:30:07 +0200,
Kim, Milo wrote:
> 
> Hi Takashi,
> 
> On 9/7/2015 11:19 PM, Jacek Anaszewski wrote:
> > Hi Takashi,
> >
> > Thanks for chasing this.
> > Milo, could you express your opinion?
> >
> > On 09/07/2015 02:25 PM, Takashi Iwai wrote:
> >> The commit [b67893206fc0: leds:lp55xx: fix firmware loading error]
> >> tries to address the firmware file handling with user helper, but it
> >> sets a wrong Kconfig CONFIG_FW_LOADER_USER_HELPER_FALLBACK.  Since the
> >> wrong option was enabled, the system got a regression -- it suffers
> >> from the unexpected long delays for non-present firmware files.
> >>
> >> This patch corrects the Kconfig dependency to the right one,
> >> CONFIG_FW_LOADER_USER_HELPER.  This doesn't change the fallback
> >> behavior but only enables UMH when needed.
> >>
> >> Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=944661
> >> Fixes: b67893206fc0 ('leds:lp55xx: fix firmware loading error')
> >> Cc: <stable@vger.kernel.org> # v4.2+
> >> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> >> ---
> >>    drivers/leds/Kconfig | 2 +-
> >>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
> >> index 70f4255ff291..2ba52bc2e174 100644
> >> --- a/drivers/leds/Kconfig
> >> +++ b/drivers/leds/Kconfig
> >> @@ -229,7 +229,7 @@ config LEDS_LP55XX_COMMON
> >>    	tristate "Common Driver for TI/National LP5521/5523/55231/5562/8501"
> >>    	depends on LEDS_LP5521 || LEDS_LP5523 || LEDS_LP5562 || LEDS_LP8501
> >>    	select FW_LOADER
> >> -	select FW_LOADER_USER_HELPER_FALLBACK
> >> +	select FW_LOADER_USER_HELPER
> >>    	help
> >>    	  This option supports common operations for LP5521/5523/55231/5562/8501
> >>    	  devices.
> 
> Thank for catching this. It seems I misunderstood firmware helper 
> configuration. LP55xx driver uses firmware interface to activate LED 
> visual effect. So this driver enables FW_LOADER_USER_HELPER_FALLBACK and 
> calls request_firmware_nowait() without uevent. Then, it will try to 
> load raw data manually when binary(firmware) file doesn't exist.
> 
> I'm still not clear what the difference is between FW_LOADER_USER_HELPER 
> and FW_LOADER_USER_HELPER_FALLBACK. Kconfig description makes me confused.
> Could you explain it in more details?

FW_LOADER_USER_HELPER_FALLBACK globally enables the fallback to user
helper mode when no file is loaded by the direct f/w loader.  It
automatically sets FW_LOADER_USER_HELPER.

OTOH, when FW_LOADER_USER_HELPER is set, requeset_firmware_nowait()
does user mode fallback only when uevent (the second) argument is
false.  Note that this is a special case.  In the usual cases --
uevent = true or request_firmware() -- its doesn't enable the
fallback.

The fallback to user helper mode is bad for the recent udev, since
udev already dropped the f/w support code completely.  Thus every
non-existing f/w load will result in 60 seconds stall.

In short, FW_LOAD_USER_HELPER_FALLBACK is present mostly only for
older systems, just for compatibility.  For drivers that need the no
direct f/w load and no udev interaction, set FW_LOAD_USER_HELPER
instead.


Takashi