linux-kernel - Re: [PATCH V4 4/9] ASoC: amd: ps: add SoundWire dma driver dma ops

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Date:   Thu, 15 Jun 2023 18:21:55 +0200
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     "Mukunda,Vijendar" <vijendar.mukunda@....com>, broonie@...nel.org
Cc:     alsa-devel@...a-project.org, Basavaraj.Hiregoudar@....com,
        Sunil-kumar.Dommati@....com, Mastan.Katragadda@....com,
        Arungopal.kondaveeti@....com, mario.limonciello@....com,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Syed Saba Kareem <Syed.SabaKareem@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 4/9] ASoC: amd: ps: add SoundWire dma driver dma ops



On 6/13/23 09:00, Mukunda,Vijendar wrote:
> On 12/06/23 23:36, Pierre-Louis Bossart wrote:
>>> +#define SDW_PLAYBACK_MIN_NUM_PERIODS    2
>>> +#define SDW_PLAYBACK_MAX_NUM_PERIODS    8
>>> +#define SDW_PLAYBACK_MAX_PERIOD_SIZE    8192
>> that's a fairly small max period. That's 21ms for 2ch S32_LE 48kHz.
>>
>> Does this come from specific limitations or is this an arbitrary number?
>>
>> A comment on this wouldn't hurt.
> This is the initial version. We haven't exercised different sample
> rates/bit depth combinations much. Currently, targeted for 2Ch, 48Khz,
> 16bit audio streams only with 64k as buffer size.
> 
> We will extend support for different sample rates/bit depths combinations
> in the future.
>>> +static u32 sdw0_dma_enable_reg[ACP63_SDW0_DMA_MAX_STREAMS] = {
>>> +	ACP_SW0_AUDIO0_TX_EN,
>>> +	ACP_SW0_AUDIO1_TX_EN,
>>> +	ACP_SW0_AUDIO2_TX_EN,
>>> +	ACP_SW0_AUDIO0_RX_EN,
>>> +	ACP_SW0_AUDIO1_RX_EN,
>>> +	ACP_SW0_AUDIO2_RX_EN,
>>> +};
>>> +
>>> +static u32 sdw1_dma_enable_reg[ACP63_SDW1_DMA_MAX_STREAMS] = {
>>> +	ACP_SW1_AUDIO1_TX_EN,
>>> +	ACP_SW1_AUDIO1_RX_EN,
>>> +};
>> Still no explanation as to why SDW0 indices start at zero and SDW1
>> indices start at one?
> We have already provided reply in previous thread, i.e. for v3 patch set.
> 
> https://lore.kernel.org/alsa-devel/de3c86cc-6cba-0cbd-0e04-43711b4c9bc2@amd.com/

That reply was

"
Currently, SDW0 instance uses 3 TX, 3 RX  ports whereas SDW1 instance
uses 1 TX, 1 RX ports.

For SDW1 instance, It uses AUDIO1 register set as per our register spec.
We have mantained similar mapping convention here for enums as well.
"

It wouldn't hurt to add a comment in the code to remind the reviewer
that this is intentional and aligned with the hardware documentation.


>>> +static int acp63_sdw_dma_open(struct snd_soc_component *component,
>>> +			      struct snd_pcm_substream *substream)
>>> +{
>>> +	struct snd_pcm_runtime *runtime;
>>> +	struct acp_sdw_dma_stream *stream;
>>> +	struct snd_soc_dai *cpu_dai;
>>> +	struct amd_sdw_manager *amd_manager;
>>> +	struct snd_soc_pcm_runtime *prtd = substream->private_data;
>>> +	int ret;
>>> +
>>> +	runtime = substream->runtime;
>>> +	cpu_dai = asoc_rtd_to_cpu(prtd, 0);
>>> +	amd_manager = snd_soc_dai_get_drvdata(cpu_dai);
>>> +	stream = kzalloc(sizeof(*stream), GFP_KERNEL);
>>> +	if (!stream)
>>> +		return -ENOMEM;
>>> +
>>> +	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>>> +		runtime->hw = acp63_sdw_hardware_playback;
>>> +	else
>>> +		runtime->hw = acp63_sdw_hardware_capture;
>>> +	ret = snd_pcm_hw_constraint_integer(runtime,
>>> +					    SNDRV_PCM_HW_PARAM_PERIODS);
>>> +	if (ret < 0) {
>>> +		dev_err(component->dev, "set integer constraint failed\n");
>>> +		kfree(stream);
>>> +		return ret;
>>> +	}
>> it's not clear to me why you have to add this specific constraint, isn't
>> this checked already with the sdw_hardware_playback information.
> In above code, first we are assigning runtime->hw structures.
> As per our understanding, we are not assigning any hw_constraints.
> 
> This snd_pcm_hw_constraint_integer(runtime,
> SNDRV_PCM_HW_PARAM_PERIODS) constraint assures that the number
> of periods is integer, hence the buffer size is aligned with the period size.

This is surprising, I thought this was already ensured by the hw_info stuff?

>>> +static u64 acp63_sdw_get_byte_count(struct acp_sdw_dma_stream *stream, void __iomem *acp_base)
>>> +{
>>> +	union acp_sdw_dma_count byte_count;
>>> +	u32 pos_low_reg, pos_high_reg;
>>> +
>>> +	byte_count.bytescount = 0;
>>> +	switch (stream->instance) {
>>> +	case ACP_SDW0:
>>> +		pos_low_reg = sdw0_dma_ring_buf_reg[stream->stream_id].pos_low_reg;
>>> +		pos_high_reg = sdw0_dma_ring_buf_reg[stream->stream_id].pos_high_reg;
>>> +		break;
>>> +	case ACP_SDW1:
>>> +		pos_low_reg = sdw1_dma_ring_buf_reg[stream->stream_id].pos_low_reg;
>>> +		pos_high_reg = sdw1_dma_ring_buf_reg[stream->stream_id].pos_high_reg;
>>> +		break;
>>> +	default:
>>> +		return -EINVAL;
>> returning -EINVAL as a u64 doesn't seem quite right to me?
> Agreed. Default case needs to be corrected. In case of invalid
> SDW instance, it should return default byte count which is zero
> instead of returning -EINVAL.
> 
> We have identified similar fix has to be implemented in our other
> dma driver as well.
> https://elixir.bootlin.com/linux/v6.4-rc6/source/sound/soc/amd/acp/amd.h#L174
> 
> Will push a supplement patch to fix it at one go.

ok