linux-kernel - Re: [PATCH] BUG-REPORT: snd-hda: hacked-together EPROBE

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Message-ID: <s5hbmphs6il.wl-tiwai@suse.de>
Date:   Wed, 21 Jun 2017 17:30:10 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Chris Wilson" <chris@...is-wilson.co.uk>
Cc:     "Intel Graphics Development" <intel-gfx@...ts.freedesktop.org>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>,
        "Guneshwor Singh" <guneshwor.o.singh@...el.com>,
        "Hardik T Shah" <hardik.t.shah@...el.com>,
        "Libin Yang" <libin.yang@...el.com>,
        "Subhransu S. Prusty" <subhransu.s.prusty@...el.com>,
        "Vinod Koul" <vinod.koul@...el.com>,
        "Julia Lawall" <Julia.Lawall@...6.fr>,
        "Jaroslav Kysela" <perex@...ex.cz>, <tiwai@...e.de>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] BUG-REPORT: snd-hda: hacked-together EPROBE_DEFER support

On Wed, 21 Jun 2017 17:23:57 +0200,
Chris Wilson wrote:
> 
> Quoting Daniel Vetter (2017-06-21 16:08:54)
> > So back when the i915 power well support landed in
> > 
> > commit 99a2008d0b32d72dfc2a54e7be1eb698dd2e3bd6
> > Author: Wang Xingchao <xingchao.wang@...ux.intel.com>
> > Date:   Thu May 30 22:07:10 2013 +0800
> > 
> >     ALSA: hda - Add power-welll support for haswell HDA
> > 
> > the logic to handle the cross-module depencies was hand-rolled using a
> > async work item, and that just doesn't work.
> > 
> > The correct way to handle cross-module deps is either:
> > - request_module + failing when the other module isn't there
> > 
> > OR
> > 
> > - failing the module load with EPROBE_DEFER.
> > 
> > You can't mix them, if you do then the entire load path just
> > busy-spins blowing through cpu cycles forever with no way to stop
> > this.
> > 
> > snd-hda-intel does mix it, because the hda codec drivers are loaded
> > using request_module, but the i915 depency is handled using
> > PROBE_DEFER (or well, should be, but I haven't found any code at all).
> > This is a major pain when trying to debug i915 load failures.
> > 
> > This patch here is a horrible hackish attempt at somewhat correctly
> > wriing EPROBE_DEFER through. Stuff that's missing:
> > - Check all the other places where load errors are conveniently
> >   dropped on the floor.
> > - Also fix up the firmware_cb path.
> > - Drop the debug noise I've left in to make it clear this isn't
> >   anything for merging.
> 
> This tames "hdaudio hdaudioC0D0: Unable to bind the codec" which was
> continuously spewing previously, and now the system is usable again.

Could you give a failing scenario?  I'm not opposing to the suggested
solution, we need to fix the mess in anyway, but I just would like to
know how to trigger the problem easily.


thanks,

Takashi