linux-kernel - Re: [PATCH] ASoC: stm32: sai: Use of_device_get_match

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Date:   Mon, 23 May 2022 15:28:48 +0200
From:   Olivier MOYSAN <olivier.moysan@...s.st.com>
To:     Tang Bin <tangbin@...s.chinamobile.com>,
        <arnaud.pouliquen@...s.st.com>, <lgirdwood@...il.com>,
        <broonie@...nel.org>, <perex@...ex.cz>, <tiwai@...e.com>,
        <mcoquelin.stm32@...il.com>, <alexandre.torgue@...s.st.com>
CC:     <alsa-devel@...a-project.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: stm32: sai: Use of_device_get_match_data() to
 simplify code

Hello Tang,

Thanks for the patch. Unfortunately this patch introduces a regression.

In the SAI driver of_device_id struct the data is a simple enum cast to 
void* pointer.
static const struct of_device_id stm32_sai_sub_ids[] = {
	  .data = (void *)STM_SAI_A_ID},

This data is an ID which can be set to 0x0.
Here we have no way to know to discriminate between an error returned by 
of_device_get_match_data() or a data id set to 0x0.

The current patch requires a change in the driver.
Either changing STM_SAI_x_ID enums, or replacing data by a struct.
For instance:
struct stm32_sai_comp_data {
	unsigned int id;
}
struct stm32_sai_comp_data stm32_sai_comp_data_a = {
	.id = STM_SAI_A_ID;
}
struct of_device_id stm32_sai_sub_ids[] = {
	.data = &stm32_sai_comp_data_a},
}

Regards
Olivier

On 5/19/22 14:42, Tang Bin wrote:
> Retrieve of match data, it's better and cleaner to use
> 'of_device_get_match_data' over 'of_match_device'.
> 
> Signed-off-by: Tang Bin <tangbin@...s.chinamobile.com>
> ---
>   sound/soc/stm/stm32_sai_sub.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/soc/stm/stm32_sai_sub.c b/sound/soc/stm/stm32_sai_sub.c
> index dd636af81..d300605a2 100644
> --- a/sound/soc/stm/stm32_sai_sub.c
> +++ b/sound/soc/stm/stm32_sai_sub.c
> @@ -1500,7 +1500,6 @@ static int stm32_sai_sub_parse_of(struct platform_device *pdev,
>   static int stm32_sai_sub_probe(struct platform_device *pdev)
>   {
>   	struct stm32_sai_sub_data *sai;
> -	const struct of_device_id *of_id;
>   	const struct snd_dmaengine_pcm_config *conf = &stm32_sai_pcm_config;
>   	int ret;
>   
> @@ -1508,10 +1507,9 @@ static int stm32_sai_sub_probe(struct platform_device *pdev)
>   	if (!sai)
>   		return -ENOMEM;
>   
> -	of_id = of_match_device(stm32_sai_sub_ids, &pdev->dev);
> -	if (!of_id)
> +	sai->id = (uintptr_t)of_device_get_match_data(&pdev->dev);
> +	if (!sai->id)
>   		return -EINVAL;
> -	sai->id = (uintptr_t)of_id->data;
>   
>   	sai->pdev = pdev;
>   	mutex_init(&sai->ctrl_lock);