linux-kernel - Re: [RFC PATCH v2 3/3] ASoC: fsl_asrc_dma: Reuse the dma channel if available in Back-End

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Date:   Thu, 11 Jun 2020 22:02:46 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>,
        Linux-ALSA <alsa-devel@...a-project.org>, lars@...afoo.de,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org, Liam Girdwood <lgirdwood@...il.com>,
        Takashi Iwai <tiwai@...e.com>, Mark Brown <broonie@...nel.org>,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [RFC PATCH v2 3/3] ASoC: fsl_asrc_dma: Reuse the dma channel if
 available in Back-End

On Fri, Jun 12, 2020 at 10:17:08AM +0800, Shengjiu Wang wrote:

> > > diff --git a/sound/soc/fsl/fsl_asrc_common.h b/sound/soc/fsl/fsl_asrc_common.h

> > > + * @req_dma_chan_dev_to_dev: flag for release dev_to_dev chan
> >
> > Since we only have dma_request call for back-end only:
> > + * @req_dma_chan: flag to release back-end dma chan
> 
> I prefer to use the description "flag to release dev_to_dev chan"
> because we won't release the dma chan of the back-end. if the chan
> is from the back-end, it is owned by the back-end component.

TBH, it just looks too long. But I wouldn't have problem if you
insist so.

> > > @@ -273,19 +299,21 @@ static int fsl_asrc_dma_hw_params(struct snd_soc_component *component,
> > >  static int fsl_asrc_dma_hw_free(struct snd_soc_component *component,
> > >                               struct snd_pcm_substream *substream)
> > >  {
> > > +     bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
> > >       struct snd_pcm_runtime *runtime = substream->runtime;
> > >       struct fsl_asrc_pair *pair = runtime->private_data;
> > > +     u8 dir = tx ? OUT : IN;
> > >
> > >       snd_pcm_set_runtime_buffer(substream, NULL);
> > >
> > > -     if (pair->dma_chan[IN])
> > > -             dma_release_channel(pair->dma_chan[IN]);
> > > +     if (pair->dma_chan[!dir])
> > > +             dma_release_channel(pair->dma_chan[!dir]);
> > >
> > > -     if (pair->dma_chan[OUT])
> > > -             dma_release_channel(pair->dma_chan[OUT]);
> > > +     if (pair->dma_chan[dir] && pair->req_dma_chan_dev_to_dev)
> > > +             dma_release_channel(pair->dma_chan[dir]);
> >
> > Why we only apply this to one direction?
> 
> if the chan is from the back-end, it is owned by the back-end
> component, so it should be released by the back-end component,
> not here. That's why I added the flag "req_dma_chan".

Ah...I forgot the IN and OUT is for front-end and back-end. The
naming isn't very good indeed. Probably we should add a line of
comments somewhere as a reminder.

Thanks