Re: [PATCH] sound: sof: ioc4-topology: avoid extra dai_params copy

[Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>]

On 8/7/24 10:02, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> The snd_pcm_hw_params structure is really too large to fit on the
> stack. Because of the way that clang inlines functions, it ends up
> twice in one function, which exceeds the 1024 byte limit for 32-bit
> architecutes:
> 
> sound/soc/sof/ipc4-topology.c:1700:1: error: stack frame size (1304) exceeds limit (1024) in 'sof_ipc4_prepare_copier_module' [-Werror,-Wframe-larger-than]
> sof_ipc4_prepare_copier_module(struct snd_sof_widget *swidget,
> 
>>From what I can tell, this was unintentional, as both
> sof_ipc4_prepare_dai_copier() and sof_ipc4_prepare_copier_module() make a
> copy for the same purpose, but copying it once has the exact same effect.

Humm, not sure. I think the copy was intentional so that if one of the
fixups fails, then the initial hw_params structure is not modified.

Also not sure why a compiler would think inlining such a large function
is a good idea?

Probably need Ranjani, Peter and Bard to comment on the format handling.


> Remove the extra copy and change the direct struct assignment to
> an explicit memcpy() call to make it clearer to the reader that this
> is what happens. Note that gcc treats struct assignment as a memcpy()
> that may be inlined anyway, so the resulting object code is the same.
> 
> Fixes: f9209644ae76 ("ASoC: SOF: ipc4-topology: Correct DAI copier config and NHLT blob request")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  sound/soc/sof/ipc4-topology.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/sound/soc/sof/ipc4-topology.c b/sound/soc/sof/ipc4-topology.c
> index 87be7f16e8c2..77f6850010f6 100644
> --- a/sound/soc/sof/ipc4-topology.c
> +++ b/sound/soc/sof/ipc4-topology.c
> @@ -1651,7 +1651,6 @@ sof_ipc4_prepare_dai_copier(struct snd_sof_dev *sdev, struct snd_sof_dai *dai,
>  			    struct snd_pcm_hw_params *params, int dir)
>  {
>  	struct sof_ipc4_available_audio_format *available_fmt;
> -	struct snd_pcm_hw_params dai_params = *params;
>  	struct sof_ipc4_copier_data *copier_data;
>  	struct sof_ipc4_pin_format *pin_fmts;
>  	struct sof_ipc4_copier *ipc4_copier;
> @@ -1676,7 +1675,7 @@ sof_ipc4_prepare_dai_copier(struct snd_sof_dev *sdev, struct snd_sof_dai *dai,
>  		num_pin_fmts = available_fmt->num_input_formats;
>  	}
>  
> -	ret = sof_ipc4_adjust_params_to_dai_format(sdev, &dai_params, pin_fmts,
> +	ret = sof_ipc4_adjust_params_to_dai_format(sdev, params, pin_fmts,
>  						   num_pin_fmts);
>  	if (ret)
>  		return ret;
> @@ -1684,15 +1683,11 @@ sof_ipc4_prepare_dai_copier(struct snd_sof_dev *sdev, struct snd_sof_dai *dai,
>  	single_bitdepth = sof_ipc4_copier_is_single_bitdepth(sdev, pin_fmts,
>  							     num_pin_fmts);
>  	ret = snd_sof_get_nhlt_endpoint_data(sdev, dai, single_bitdepth,
> -					     &dai_params,
> +					     params,
>  					     ipc4_copier->dai_index,
>  					     ipc4_copier->dai_type, dir,
>  					     &ipc4_copier->copier_config,
>  					     &copier_data->gtw_cfg.config_length);
> -	/* Update the params to reflect the changes made in this function */
> -	if (!ret)
> -		*params = dai_params;
> -
>  	return ret;
>  }
>  
> @@ -1784,9 +1779,9 @@ sof_ipc4_prepare_copier_module(struct snd_sof_widget *swidget,
>  		 * for capture.
>  		 */
>  		if (dir == SNDRV_PCM_STREAM_PLAYBACK)
> -			ref_params = *fe_params;
> +			memcpy(&ref_params, fe_params, sizeof(ref_params));
>  		else
> -			ref_params = *pipeline_params;
> +			memcpy(&ref_params, pipeline_params, sizeof(ref_params));
>  
>  		copier_data->gtw_cfg.node_id &= ~SOF_IPC4_NODE_INDEX_MASK;
>  		copier_data->gtw_cfg.node_id |=
> @@ -1819,7 +1814,7 @@ sof_ipc4_prepare_copier_module(struct snd_sof_widget *swidget,
>  		 * In case of capture the ref_params returned will be used to
>  		 * find the input configuration of the copier.
>  		 */
> -		ref_params = *fe_params;
> +		memcpy(&ref_params, fe_params, sizeof(ref_params));
>  		ret = sof_ipc4_prepare_dai_copier(sdev, dai, &ref_params, dir);
>  		if (ret < 0)
>  			return ret;
> @@ -1829,7 +1824,7 @@ sof_ipc4_prepare_copier_module(struct snd_sof_widget *swidget,
>  		 * input configuration of the copier.
>  		 */
>  		if (dir == SNDRV_PCM_STREAM_PLAYBACK)
> -			ref_params = *pipeline_params;
> +			memcpy(&ref_params, pipeline_params, sizeof(ref_params));
>  
>  		break;
>  	}
> @@ -1838,7 +1833,7 @@ sof_ipc4_prepare_copier_module(struct snd_sof_widget *swidget,
>  		ipc4_copier = (struct sof_ipc4_copier *)swidget->private;
>  		copier_data = &ipc4_copier->data;
>  		available_fmt = &ipc4_copier->available_fmt;
> -		ref_params = *pipeline_params;
> +		memcpy(&ref_params, pipeline_params, sizeof(ref_params));
>  
>  		break;
>  	}