linux-kernel - Re: [PATCH v3 1/6] ASoC: dmaengine: do not use a NULL prepare_slave

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Date:   Wed, 20 Apr 2022 10:17:06 +0000
From:   <Codrin.Ciubotariu@...rochip.com>
To:     <sha@...gutronix.de>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <lars@...afoo.de>,
        <broonie@...nel.org>, <perex@...ex.cz>, <tiwai@...e.com>,
        <robh+dt@...nel.org>, <Nicolas.Ferre@...rochip.com>
Subject: Re: [PATCH v3 1/6] ASoC: dmaengine: do not use a NULL
 prepare_slave_config() callback

On 20.04.2022 13:06, Sascha Hauer wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Wed, Apr 20, 2022 at 09:58:06AM +0000, Codrin.Ciubotariu@...rochip.com wrote:
>> On 20.04.2022 12:15, Sascha Hauer wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> Hi,
>>
>> Hi Sascha,
>>
>>>
>>> On Mon, Mar 07, 2022 at 02:21:57PM +0200, Codrin Ciubotariu wrote:
>>>> Even if struct snd_dmaengine_pcm_config is used, prepare_slave_config()
>>>> callback might not be set. Check if this callback is set before using it.
>>>>
>>>> Fixes: fa654e085300 ("ASoC: dmaengine-pcm: Provide default config")
>>>> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
>>>> ---
>>>>
>>>> Changes in v2,v3:
>>>>    - none
>>>>
>>>>    sound/soc/soc-generic-dmaengine-pcm.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
>>>> index 285441d6aeed..2ab2ddc1294d 100644
>>>> --- a/sound/soc/soc-generic-dmaengine-pcm.c
>>>> +++ b/sound/soc/soc-generic-dmaengine-pcm.c
>>>> @@ -86,10 +86,10 @@ static int dmaengine_pcm_hw_params(struct snd_soc_component *component,
>>>>
>>>>         memset(&slave_config, 0, sizeof(slave_config));
>>>>
>>>> -     if (!pcm->config)
>>>> -             prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
>>>> -     else
>>>> +     if (pcm->config && pcm->config->prepare_slave_config)
>>>>                 prepare_slave_config = pcm->config->prepare_slave_config;
>>>> +     else
>>>> +             prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
>>>>
>>>>         if (prepare_slave_config) {
>>>>                 int ret = prepare_slave_config(substream, params, &slave_config);
>>>
>>> I wonder if this patch is correct. There are drivers like
>>> sound/soc/mxs/mxs-pcm.c which call snd_dmaengine_pcm_register() with a
>>> config which has the prepare_slave_config callback unset. For these
>>> drivers dmaengine_pcm_hw_params() previously was a no-op. Now with this
>>> patch snd_dmaengine_pcm_prepare_slave_config() and
>>> dmaengine_slave_config() are called. At least for the mxs-pcm driver
>>> calling dmaengine_slave_config() will return -ENOSYS.
>>>
>>> At least the "Check if this callback is set before using it" part is
>>> wrong, the callback is checked before using it with
>>>
>>>           if (prepare_slave_config) {
>>>                   ...
>>>           }
>>>
>>> I don't have any mxs hardware at hand to test this. I just stumbled upon
>>> the change of behaviour when rebasing
>>> https://patchwork.kernel.org/project/alsa-devel/patch/20220301122111.1073174-1-s.hauer@pengutronix.de/
>>> on current master.
>>
>> You are right. I changed the behavior from:
>> if (pmc->config && !pcm->config->prepare_slave_config)
>>        <do nothing>
>> to:
>> if (pmc->config && !pcm->config->prepare_slave_config)
>>        snd_dmaengine_pcm_prepare_slave_config()
>>
>> It was not intended and I agree that the commit message is not accurate.
>> I guess some drivers might not need dmaengine_slave_config()...
>> However, in my case, for the mchp-pdmc driver, I do have pcm->config
>> with pcm->config->prepare_slave_config NULL, but I still need
>> snd_dmaengine_pcm_prepare_slave_config() to be called. Should we add a
>> separate flag to call snd_dmaengine_pcm_prepare_slave_config() if
>> pcm->config->prepare_slave_config is NULL?
> 
> Other drivers set pcm->config->prepare_slave_config to
> snd_dmaengine_pcm_prepare_slave_config() explicitly:
> 
> sound/soc/fsl/imx-pcm-dma.c:33: .prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config,
> 
> I think that's the way to go.

That's more elegant, right. I will revert this patch and use your 
suggestion for the mchp-pdmc driver.

Thanks and best regards,
Codrin