linux-kernel - Re: [PATCH v2] DMA: OMAP: fix OMAP1510 incorrect residue

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Date:   Tue, 5 Jun 2018 15:56:37 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Vinod Koul <vkoul@...nel.org>
CC:     <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        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] DMA: OMAP: fix OMAP1510 incorrect residue_granularity

On 06/02/2018 06:27 PM, 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).

Good catch.

can you fix up the subject:
dmaengine: ti: omap-dma: Fix OMAP1510...


Otherwise:
Acked-by: Peter Ujfalusi <peter.ujfalusi@...com>

> 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.
> 
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> ---
> Changelog:
> v2: apply the patch against omap-dma.c moved to drivers/dma/ti/
> 
>  drivers/dma/ti/omap-dma.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/ti/omap-dma.c b/drivers/dma/ti/omap-dma.c
> index b73fb51fbc81..96b5096c26dd 100644
> --- a/drivers/dma/ti/omap-dma.c
> +++ b/drivers/dma/ti/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);
> 


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