Re: [alsa-devel] [PATCH] ASoC: core: Invoke pcm_new() for all DAI-link

[Rohit Kumar]

Hello Arnaud,


On 11/5/2018 4:43 PM, Arnaud Pouliquen wrote:
> Hello Rohit,
>
> On 11/2/18 1:06 PM, Rohit Kumar wrote:
> > On 11/2/2018 1:12 PM, Takashi Iwai wrote:
> > > On Thu, 01 Nov 2018 13:38:49 +0100,
> > > Rohit kumar wrote:
> > > > Remove no_pcm check to invoke pcm_new() for backend dai-links
> > > > too. This fixes crash in hdmi codec driver during hdmi_codec_startup()
> > > > while accessing chmap_info struct. chmap_info struct memory is
> > > > allocated in pcm_new() of hdmi codec driver which is not invoked
> > > > in case of DPCM when hdmi codec driver is part of backend dai-link.
> > > >
> > > > Below is the crash stack:
> > > >
> > > > [ÂÂ 61.635493] Unable to handle kernel NULL pointer dereference at
> > > > virtual address 00000018
> > > > ..
> > > > [ÂÂ 61.666696]ÂÂ CM = 0, WnR = 1
> > > > [ÂÂ 61.669778] user pgtable: 4k pages, 39-bit VAs, pgd =
> > > > ffffffc0d6633000
> > > > [ÂÂ 61.676526] [0000000000000018] *pgd=0000000153fc8003,
> > > > *pud=0000000153fc8003, *pmd=0000000000000000
> > > > [ÂÂ 61.685793] Internal error: Oops: 96000046 [#1] PREEMPT SMP
> > > > [ÂÂ 61.722955] CPU: 7 PID: 2238 Comm: aplay Not tainted 4.14.72 #21
> > > > ..
> > > > [ÂÂ 61.740269] PC is at hdmi_codec_startup+0x124/0x164
> > > > [ÂÂ 61.745308] LR is at hdmi_codec_startup+0xe4/0x164
> > > >
> > > > Signed-off-by: Rohit kumar <rohitkr@xxxxxxxxxxxxxx>
> > > Did you check whether all drivers have no side-effect by this change?
> > > The hdmi-codec isn't the only driver that has pcm_new ops, so we have
> > > to make sure that such a fundamental change wouldn't bring any
> > > regressions.
> > Below are the drivers calling pcm_new() other than hdmi codec driver.
> > sound/soc/meson/axg-frddr.c
> > sound/soc/meson/axg-toddr.c
> > These two drivers are frontend DAI drivers and should not be impacted
> > because of this.
> >
> > Other than this, pcm_new() is called from sound/soc/stm/stm32_sai_sub.c
> > I could not get much info about this driver. However, it is just adding
> > kcontrols in pcm_new() which uses internal private structs in get()/put().
> > Olivier Moysan can too confirm on this.
> First, i'm answering  for Olivier: no regression identified for the SAI
> driver, it is not a DPCM driver.
>
> Then i have a concern about the call of pcm_new for a no-PCM backend.
> Does it make sense? In DPCM concept, the backend is not linked to the
> PCM device...
>
> Instead, I would suggest that you add protection in HDMI_codec on
> chmap_info pointer.
>
> The drawback would be that the control is no more available...do you
> need it?
I don't need chmap_info, but ELD kcontrol is also defined in pcm_new() which
we need. We should probably update the driver to make it compatible with
DPCM. Any suggestions?
> Regards
> Arnaud
>
> > Thanks,
> > Rohit
> > > thanks,
> > >
> > > Takashi
Thanks,
Rohit

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