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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>, <lgirdwood@gmail.com>,
        <plai@codeaurora.org>, <linux-kernel@vger.kernel.org>,
        <tiwai@suse.com>, <broonie@kernel.org>,
        <srinivas.kandagatla@linaro.org>
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From:   Arnaud Pouliquen <arnaud.pouliquen@st.com>
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Message-ID: <4f22e4e5-84f0-1560-1ba7-5e77d44fd312@st.com>
Date:   Tue, 6 Nov 2018 16:41:23 +0100
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Hello Rohit

On 11/5/18 7:14 PM, Rohit Kumar wrote:
> 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:
>>>>>
>>>>> [   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?
> 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?

I would say force device to 0 if no_pcm (need probably to create the
control in hdmi_of_xlate_dai_id instead of hdmi_codec_pcm_new).
But keep in mind that solution has to work in case of multi HDMI codec
instances, perhaps using prefix...
Anyway, i'm not a DPCM expert so perhaps more elegant solutions exist.

Regards
Arnaud

>> Regards
>> Arnaud
>>
>>> Thanks,
>>> Rohit
>>>> thanks,
>>>>
>>>> Takashi
> Thanks,
> Rohit
>