[PATCH] ASoC: dmaengine: Document support for TX only or RX only streams

[Mark Brown]

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 at intel.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
---
 sound/soc/soc-generic-dmaengine-pcm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
index fb95c1464e66..9ef80a48707e 100644
--- 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;
-- 
2.20.1