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

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Date:	Tue, 08 Sep 2015 09:37:35 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	"Kim, Milo" <milo.kim@...com>, linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
	Bryan Wu <cooloney@...il.com>
Subject: Re: [PATCH] leds:lp55xx: Correct Kconfig dependency for f/w user helper

On 09/08/2015 07:06 AM, Takashi Iwai wrote:
> 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@...r.kernel.org> # v4.2+
>>>> Signed-off-by: Takashi Iwai <tiwai@...e.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.

Merged to fixes-for-4.3 branch of linux-leds.git.
Thanks for this explanation.

-- 
Best Regards,
Jacek Anaszewski
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