linux-imx

dmaengine: ti: omap-dma: Fix OMAP1510 incorrect residue_granularity

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/ti/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 DMA engine.

Let's do the latter.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>