linux-kernel - Re: [alsa-devel] [RFC PATCH 31/40] soundwire: intel: move shutdown() callback and don't export symbol

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Message-ID: <20190823073407.GF2672@vkoul-mobl>
Date:   Fri, 23 Aug 2019 13:04:07 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Cezary Rojewski <cezary.rojewski@...el.com>, tiwai@...e.de,
        gregkh@...uxfoundation.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, broonie@...nel.org,
        srinivas.kandagatla@...aro.org, jank@...ence.com,
        slawomir.blauciak@...el.com, Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [RFC PATCH 31/40] soundwire: intel: move shutdown()
 callback and don't export symbol

On 14-08-19, 14:31, Pierre-Louis Bossart wrote:
> 
> 
> > > > > +void intel_shutdown(struct snd_pcm_substream *substream,
> > > > > +            struct snd_soc_dai *dai)
> > > > > +{
> > > > > +    struct sdw_cdns_dma_data *dma;
> > > > > +
> > > > > +    dma = snd_soc_dai_get_dma_data(dai, substream);
> > > > > +    if (!dma)
> > > > > +        return;
> > > > > +
> > > > > +    snd_soc_dai_set_dma_data(dai, substream, NULL);
> > > > > +    kfree(dma);
> > > > > +}
> > > > 
> > > > Correct me if I'm wrong, but do we really need to _get_dma_ here?
> > > > _set_dma_ seems bulletproof, same for kfree.
> > > 
> > > I must admit I have no idea why we have a reference to DMAs here, this looks
> > > like an abuse to store a dai-specific context, and the initial test looks
> > > like copy-paste to detect invalid configs, as done in other callbacks. Vinod
> > > and Sanyog might have more history than me here.
> > 
> > I dont see snd_soc_dai_set_dma_data() call for
> > sdw_cdns_dma_data so somthing is missing (at least in upstream code)
> > 
> > IIRC we should have a snd_soc_dai_set_dma_data() in alloc or some
> > initialization routine and we free it here.. Sanyog?
> 
> Vinod, I double-checked that we do not indeed have a call to
> snd_soc_dai_dma_data(), but there is code in cdns_set_stream() that sets the
> relevant dai->playback/capture_dma_data, see below
> 
> I am not a big fan of this code, touching the ASoC core internal fields
> isn't a good idea in general.

IIRC as long as you stick to single link I do not see this required. The
question comes into picture when we have multi links as you would need
to allocate a soundwire stream and set that for all the sdw DAIs

So, what is the current model of soundwire stream, which entity allocates
that and do you still care about multi-link? is there any machine driver
with soundwire upstream yet?

> Also not sure why for a DAI we need both _drvdata and _dma_data (especially

_drvdata is global for driver whereas _dma_data is typically used per
DAI

> for this case where the information stored has absolutely nothing to do with
> DMAs).
> 
> If the idea was to keep a context that is direction-dependent, that's likely
> unnecessary. For the Intel/Cadence case the interfaces can be configured as
> playback OR capture, not both concurrently, so the "dma" information could
> have been stored in the generic DAI _drvdata.
> 
> I have other things to look into for now but this code will likely need to
> be cleaned-up at some point to remove unnecessary parts.

Sure please go ahead and do the cleanup.
> 
> int cdns_set_sdw_stream(struct snd_soc_dai *dai,
> 			void *stream, bool pcm, int direction)
> {
> 	struct sdw_cdns *cdns = snd_soc_dai_get_drvdata(dai);
> 	struct sdw_cdns_dma_data *dma;
> 
> 	dma = kzalloc(sizeof(*dma), GFP_KERNEL);
> 	if (!dma)
> 		return -ENOMEM;
> 
> 	if (pcm)
> 		dma->stream_type = SDW_STREAM_PCM;
> 	else
> 		dma->stream_type = SDW_STREAM_PDM;
> 
> 	dma->bus = &cdns->bus;
> 	dma->link_id = cdns->instance;
> 
> 	dma->stream = stream;
> 
> >>> this is equivalent to snd_soc_dai_dma_data()
> 
> 	if (direction == SNDRV_PCM_STREAM_PLAYBACK)
> 		dai->playback_dma_data = dma;
> 	else
> 		dai->capture_dma_data = dma;
> <<<<
> 	return 0;
> }
> EXPORT_SYMBOL(cdns_set_sdw_stream);

-- 
~Vinod