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Subject: Re: [alsa-devel] [PATCH] ASoC: core: Invoke pcm_new() for all
 DAI-link
To:     Rohit Kumar <rohitkr@codeaurora.org>, Takashi Iwai <tiwai@suse.de>,
        <olivier.moysan@st.com>
CC:     <rohkumar@qti.qualcomm.com>, <alsa-devel@alsa-project.org>,
        <bgoswami@codeaurora.org>, <linux-kernel@vger.kernel.org>,
        <plai@codeaurora.org>, <tiwai@suse.com>, <lgirdwood@gmail.com>,
        <broonie@kernel.org>, <srinivas.kandagatla@linaro.org>
References: <1541075929-29323-1-git-send-email-rohitkr@codeaurora.org>
 <s5htvl0exil.wl-tiwai@suse.de>
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From:   Arnaud Pouliquen <arnaud.pouliquen@st.com>
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Message-ID: <791d4587-4db3-3ffa-331a-f79d0993ca8c@st.com>
Date:   Mon, 5 Nov 2018 12:13:20 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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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:
>>>
>>> [   61.635493] Unable to handle kernel NULL pointer dereference at
>>> virtual address 00000018
>>> ..
>>> [   61.666696]   CM = 0, WnR = 1
>>> [   61.669778] user pgtable: 4k pages, 39-bit VAs, pgd =
>>> ffffffc0d6633000
>>> [   61.676526] [0000000000000018] *pgd=0000000153fc8003,
>>> *pud=0000000153fc8003, *pmd=0000000000000000
>>> [   61.685793] Internal error: Oops: 96000046 [#1] PREEMPT SMP
>>> [   61.722955] CPU: 7 PID: 2238 Comm: aplay Not tainted 4.14.72 #21
>>> ..
>>> [   61.740269] PC is at hdmi_codec_startup+0x124/0x164
>>> [   61.745308] LR is at hdmi_codec_startup+0xe4/0x164
>>>
>>> Signed-off-by: Rohit kumar <rohitkr@codeaurora.org>
>> 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?

Regards
Arnaud

> 
> Thanks,
> Rohit
>> thanks,
>>
>> Takashi
>