ASoC: generic-dmaengine-pcm: Check DMA residue granularity

The dmaengine framework now exposes the granularity with which it is able to
report the transfer residue for a certain DMA channel. Check the granularity in
the generic dmaengine PCM driver and
	a) Set the SNDRV_PCM_INFO_BATCH if the granularity is per period or worse.
	b) Fallback to the (race condition prone) period counting if the driver does
	not support any residue reporting.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
index 4e2bed89a4a4..560a7787d8a7 100644
--- a/sound/soc/soc-generic-dmaengine-pcm.c
+++ b/sound/soc/soc-generic-dmaengine-pcm.c
@@ -144,6 +144,8 @@ static int dmaengine_pcm_set_runtime_hwparams(struct snd_pcm_substream *substrea
         if (ret == 0) {
                 if (dma_caps.cmd_pause)
                         hw.info |= SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME;
+                if (dma_caps.residue_granularity <= DMA_RESIDUE_GRANULARITY_SEGMENT)
+                        hw.info |= SNDRV_PCM_INFO_BATCH;
         }
 
         return snd_soc_set_runtime_hwparams(substream, &hw);
@@ -187,6 +189,21 @@ static struct dma_chan *dmaengine_pcm_compat_request_channel(
                                                  dma_data->filter_data);
 }
 
+static bool dmaengine_pcm_can_report_residue(struct dma_chan *chan)
+{
+        struct dma_slave_caps dma_caps;
+        int ret;
+
+        ret = dma_get_slave_caps(chan, &dma_caps);
+        if (ret != 0)
+                return true;
+
+        if (dma_caps.residue_granularity == DMA_RESIDUE_GRANULARITY_DESCRIPTOR)
+                return false;
+
+        return true;
+}
+
 static int dmaengine_pcm_new(struct snd_soc_pcm_runtime *rtd)
 {
         struct dmaengine_pcm *pcm = soc_platform_to_pcm(rtd->platform);
@@ -239,6 +256,16 @@ static int dmaengine_pcm_new(struct snd_soc_pcm_runtime *rtd)
                                 max_buffer_size);
                 if (ret)
                         goto err_free;
+
+                /*
+                 * This will only return false if we know for sure that at least
+                 * one channel does not support residue reporting. If the DMA
+                 * driver does not implement the slave_caps API we rely having
+                 * the NO_RESIDUE flag set manually in case residue reporting is
+                 * not supported.
+                 */
+                if (!dmaengine_pcm_can_report_residue(pcm->chan[i]))
+                        pcm->flags |= SND_DMAENGINE_PCM_FLAG_NO_RESIDUE;
         }
 
         return 0;