linux-kernel - Re: [PATCH v2] dmaengine: ti: omap-dma: Fix OMAP1510 incorrect residue

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Date:   Tue, 19 Jun 2018 09:59:08 +0530
From:   Vinod <vkoul@...nel.org>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Jarkko Nikula <jarkko.nikula@...mer.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-omap@...r.kernel.org, Aaro Koskinen <aaro.koskinen@....fi>,
        Tony Lindgren <tony@...mide.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] dmaengine: ti: omap-dma: Fix OMAP1510 incorrect
 residue_granularity

On 05-06-18, 18:59, Janusz Krzysztofik wrote:
> 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.
> 
> Created and tested against next-20180531 tag from linux-next tree.

This is not useful for log.

I have stripped this and applied

-- 
~Vinod