linux-kernel - Re: [PATCH V2 5/9] ASoC: amd: ps: add support for SoundWire DMA interrupts

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Date:   Wed, 31 May 2023 12:58:46 +0530
From:   "Mukunda,Vijendar" <vijendar.mukunda@....com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.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 V2 5/9] ASoC: amd: ps: add support for SoundWire DMA
 interrupts

On 24/05/23 13:15, Mukunda,Vijendar wrote:
> On 23/05/23 20:30, Pierre-Louis Bossart wrote:
>> On 5/23/23 02:36, Mukunda,Vijendar wrote:
>>> On 22/05/23 23:42, Pierre-Louis Bossart wrote:
>>>> On 5/22/23 08:31, Vijendar Mukunda wrote:
>>>>> Initialize workqueue for SoundWire DMA interrupts handling.
>>>>> Whenever audio data equal to the SoundWire FIFO watermark level
>>>>> are produced/consumed, interrupt is generated.
>>>>> Acknowledge the interrupt and schedule the workqueue.
>>>> It would help to explain why a work queue is needed is the first place,
>>>> as opposed to handling periods in the interrupt thread.
>>> For SoundWire DAI link, we are setting nonatomic flag to true.
>>> If we return period elapsed from hard irq handler instead of workqueue,
>>> soft lock up is observed during stream closure.
>>>
>>> We can use interrupt thread as well. To have a symmetry with
>>> SoundWire manager work queues, we have used workqueue for
>>> DMA interrupts.
>> Oh, I completely missed the model here.
>>
>> If you are using the bottom half/hard irq handler to read status
>> information, the natural thing to do would be to have an irq thread, no?
>>
>> Not sure I see the benefit of aligning with the manager work queues -
>> unless it makes your life simpler to avoid race conditions with
>> cancel_work_sync()?
> We can implement request_threaded_irq() and move the handling of
> DMA interrupts to thread function whereas we need to handle SoundWire
> manager interrupts in top half only. Reason as follows.
>
> As per our design, we are not masking the interrupts in top half and
> restoring mask after thread execution like Intel and
> our IP supports line based interrupts. If we move SoundWire manager
> interrupt handling to thread function, we have observed interrupts are
> reported but not handled properly due to thread execution is in progress
> sometimes.
> we will add comments for this design constraint in the code if we have to
> go with threaded_irq implementation.
>
> @Bossart: we are waiting for your reply.
>>>>> +static void acp63_sdw_dma_workthread(struct work_struct *work)
>>>>> +{
>>>>> +	struct acp63_dev_data *adata = container_of(work, struct acp63_dev_data,
>>>>> +						    acp_sdw_dma_work);
>>>>> +	struct sdw_dma_dev_data *sdw_dma_data;
>>>>> +	u32 stream_index;
>>>>> +	u16 pdev_index;
>>>>> +
>>>>> +	pdev_index = adata->sdw_dma_dev_index;
>>>>> +	sdw_dma_data = dev_get_drvdata(&adata->pdev[pdev_index]->dev);
>>>>> +
>>>>> +	for (stream_index = 0; stream_index < ACP63_SDW0_DMA_MAX_STREAMS; stream_index++) {
>>>>> +		if (adata->sdw0_dma_intr_stat[stream_index]) {
>>>>> +			if (sdw_dma_data->sdw0_dma_stream[stream_index])
>>>>> +				snd_pcm_period_elapsed(sdw_dma_data->sdw0_dma_stream[stream_index]);
>>>>> +			adata->sdw0_dma_intr_stat[stream_index] = 0;
>>>>> +		}
>>>>> +	}
>>>>> +	for (stream_index = 0; stream_index < ACP63_SDW1_DMA_MAX_STREAMS; stream_index++) {
>>>>> +		if (adata->sdw1_dma_intr_stat[stream_index]) {
>>>>> +			if (sdw_dma_data->sdw1_dma_stream[stream_index])
>>>>> +				snd_pcm_period_elapsed(sdw_dma_data->sdw1_dma_stream[stream_index]);
>>>>> +			adata->sdw1_dma_intr_stat[stream_index] = 0;
>>>>> +		}
>>>>> +	}
>>>> I am not clear on the benefits of the workqueue which only tests a flag
>>>> that's set ...
>>> In top half, we are checking all stream irq mask and setting
>>> corresponding stream id index in interrupt status array when dma
>>> irq is raised.
>>>
>>> Our intention is to handle snd_pcm_period_elapsed in process context.
>>> if the flag is set, call the period elapsed for the substream based on stream
>>> id in work queue.