ASoC: dmaengine: Document support for TX only or RX only streams

We intentionally do not return an error if we get a permanent failure
from dma_request_chan() in order to support systems which have TX only
or RX only channels. Add a comment documenting this.

Reported-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Link: https://lore.kernel.org/r/20201008161105.21804-1-broonie@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
index fb95c14..9ef80a4 100644 (file)
--- a/sound/soc/soc-generic-dmaengine-pcm.c
+++ b/sound/soc/soc-generic-dmaengine-pcm.c
@@ -386,6 +386,11 @@ static int dmaengine_pcm_request_chan_of(struct dmaengine_pcm *pcm,
                        name = config->chan_names[i];
                chan = dma_request_chan(dev, name);
                if (IS_ERR(chan)) {
+                       /*
+                        * Only report probe deferral errors, channels
+                        * might not be present for devices that
+                        * support only TX or only RX.
+                        */
                        if (PTR_ERR(chan) == -EPROBE_DEFER)
                                return -EPROBE_DEFER;
                        pcm->chan[i] = NULL;