Commit 0198d7bb8a0c ("ASoC: omap-mcbsp: Convert to use the sdma-pcm instead of omap-pcm") resulted in broken audio playback on OMAP1510 (discovered on Amstrad Delta).

When running on OMAP1510, omap-pcm used to obtain DMA offset from snd_dmaengine_pcm_pointer_no_residue() based on DMA interrupt triggered software calculations instead of snd_dmaengine_pcm_pointer() which depended on residue value calculated from omap_dma_get_src_pos(). Similar code path is still available in now used sound/soc/soc-generic-dmaengine-pcm.c but it is not triggered.

It was verified already before that omap_get_dma_src_pos() from arch/arm/plat-omap/dma.c didn't work correctly for OMAP1510 - see commit 1bdd7419910c ("ASoC: OMAP: fix OMAP1510 broken PCM pointer callback") for details. Apparently the same applies to its successor, omap_dma_get_src_pos() from drivers/dma/omap-dma.c.

On the other hand, snd_dmaengine_pcm_pointer_no_residue() is described as depreciated and discouraged for use in new drivers because of its unreliable accuracy. However, it seems the only working option for OPAM1510 now, as long as a software calculated residue is not implemented as OMAP1510 fallback in omap-dma.

Using snd_dmaengine_pcm_pointer_no_residue() code path instead of snd_dmaengine_pcm_pointer() in sound/soc/soc-generic-dmaengine-pcm.c can be triggered in two ways: - by passing pcm->flags |= SND_DMAENGINE_PCM_FLAG_NO_RESIDUE from sound/soc/omap/sdma-pcm.c, - by passing dma_caps.residue_granularity = DMA_RESIDUE_GRANULARITY_DESCRIPTOR from drivers/dma/omap-dma.c.

Let's do the latter.

Created and tested against next-20180531 tag from linux-next tree.

Signed-off-by: Janusz Krzysztofik jmkrzyszt@gmail.com --- drivers/dma/omap-dma.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c index d21c19822feb..56399bd45179 100644 --- a/drivers/dma/omap-dma.c +++ b/drivers/dma/omap-dma.c @@ -1485,7 +1485,11 @@ static int omap_dma_probe(struct platform_device *pdev) od->ddev.src_addr_widths = OMAP_DMA_BUSWIDTHS; od->ddev.dst_addr_widths = OMAP_DMA_BUSWIDTHS; od->ddev.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV); - od->ddev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST; + if (__dma_omap15xx(od->plat->dma_attr)) + od->ddev.residue_granularity = + DMA_RESIDUE_GRANULARITY_DESCRIPTOR; + else + od->ddev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST; od->ddev.max_burst = SZ_16M - 1; /* CCEN: 24bit unsigned */ od->ddev.dev = &pdev->dev; INIT_LIST_HEAD(&od->ddev.channels);