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    SubjectRe: [PATCH] ALSA: hda - Defer probe when loading patch firmware
    On Thu, Aug 09, 2012 at 09:42:48AM +0200, Takashi Iwai wrote:
    > At Thu, 9 Aug 2012 09:36:42 +0200,
    > Thierry Reding wrote:
    > >
    > > On Thu, Aug 09, 2012 at 09:31:30AM +0200, Takashi Iwai wrote:
    > > > At Thu, 9 Aug 2012 09:08:13 +0200,
    > > > Thierry Reding wrote:
    > > > >
    > > > > On Thu, Aug 09, 2012 at 08:57:13AM +0200, Takashi Iwai wrote:
    > > > > > At Thu, 9 Aug 2012 08:45:23 +0200,
    > > > > > Thierry Reding wrote:
    > > > > > >
    > > > > > > Recent changes to the firmware loading helpers cause drivers to stall
    > > > > > > when firmware is loaded during the module_init() call. The snd-hda-intel
    > > > > > > module requests firmware if the patch= parameter is used to load a patch
    > > > > > > file. This patch works around the problem by deferring the probe in such
    > > > > > > cases, which will cause the module to load successfully and the driver
    > > > > > > binding to the device outside the module_init() call.
    > > > > >
    > > > > > Is the "recent" change meant 3.6 kernel, or in linux-next?
    > > > > >
    > > > > > In anyway, I don't understand why such a change was allowed. Most
    > > > > > drivers do call request_firmware() at the device probing time.
    > > > > > If this really has to be resolved in the driver side, it must be a bug
    > > > > > in the firmware loader core code.
    > > > >
    > > > > A good explanation of the problem and subsequent discussion can be found
    > > > > here:
    > > > >
    > > > > http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/49975
    > > >
    > > > Yeah, but it doesn't justify this ugly module option.
    > > > It's a simple bug. Papering over it with this option doesn't fix
    > > > anything.
    > >
    > > It's not an option, all it does is defer probing if and only if the
    > > patch parameter was specified to make sure the firmware load won't
    > > stall. I realize that this may not be an optimal solution, but at least
    > > it fixes the problem with no fallout.
    >
    > Ah sorry, I misread the patch.
    >
    > Then it shouldn't be checked at that point. Since 3.5 kernel, the
    > probing code was already split for vga_switcheroo support.

    Yes, I saw that. But unless you actually use vga_switcheroo, the second
    stage, azx_probe_continue(), will still be called from azx_probe() and
    therefore ultimately from module_init().

    Before coming up with this patch I actually did play around a bit with
    using the asynchronous firmware load functions but it turned out to be
    rather difficult to do so I opted for the easy way. The biggest problem
    I faced was that since patch loading needs to be done very early on, a
    lot of the initialization would need to be done after .probe() and many
    things could still fail, so cleaning up after errors would become
    increasingly difficult.

    > The point you added is the second stage.

    I don't understand this sentence.

    Thierry
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