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


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