linux-kernel - Re: [PATCH 3/4] dmaengine: qcom_bam

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Date:	Wed, 2 Dec 2015 11:22:55 -0600
From:	Andy Gross <agross@...eaurora.org>
To:	Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Rob Herring <robh+dt@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Archit Taneja <architt@...eaurora.org>
Subject: Re: [PATCH 3/4] dmaengine: qcom_bam_dma: use correct pipe FIFO size

On Wed, Dec 02, 2015 at 06:44:11PM +0200, Stanimir Varbanov wrote:
> On 12/01/2015 07:23 PM, Andy Gross wrote:
> > On Tue, Dec 01, 2015 at 11:14:58AM +0200, Stanimir Varbanov wrote:
> >> The pipe fifo size register must instruct the bam hw
> >> how many hw descriptors can be pushed to fifo. Currently
> >> we isntruct the hw with 32KBytes but wrap the tail in
> >> bam_start_dma in BAM_P_EVNT_REG on 4095 i.e. 32760. This
> >> leads to stalled transactions when the tail wraps.
> >>
> >> Fix this by use the correct fifo size in BAM_P_FIFO_SIZES
> >> register i.e. 32K - 8.
> >>
> >> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
> >> ---
> >>  drivers/dma/qcom_bam_dma.c |    2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/dma/qcom_bam_dma.c b/drivers/dma/qcom_bam_dma.c
> >> index 0f06f3b7a72b..6d290de9ab2b 100644
> >> --- a/drivers/dma/qcom_bam_dma.c
> >> +++ b/drivers/dma/qcom_bam_dma.c
> >> @@ -458,7 +458,7 @@ static void bam_chan_init_hw(struct bam_chan *bchan,
> >>  	 */
> >>  	writel_relaxed(ALIGN(bchan->fifo_phys, sizeof(struct bam_desc_hw)),
> >>  			bam_addr(bdev, bchan->id, BAM_P_DESC_FIFO_ADDR));
> >> -	writel_relaxed(BAM_DESC_FIFO_SIZE,
> >> +	writel_relaxed(BAM_MAX_DATA_SIZE,
> >>  			bam_addr(bdev, bchan->id, BAM_P_FIFO_SIZES));
> > 
> > This is just using the #define.  That is ok, but if you use this instead of the
> > BAM_P_FIFO_SIZES then you need to fix your comment.  Or actually use the
> > register value.... otherwise looks fine.
> 
> I did not follow your comment, but the intension of the patch is to set
> the proper FIFO size in BAM_P_FIFO_SIZES register, i.e. 32K - 8.

Sorry, I mixed up the usage and was thinking there was something you read out
that told you the size.  That's not how it works, unfortunately.  The
MAX_DATA_SIZE is fine, but the name is a little misleading.  Perhaps just
BAM_FIFO_SIZE?


Regards,

Andy
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