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

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Message-ID: <56697BA9.5050805@linaro.org>
Date:	Thu, 10 Dec 2015 15:18:33 +0200
From:	Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:	Andy Gross <agross@...eaurora.org>,
	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 12/02/2015 07:22 PM, Andy Gross wrote:
> 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?

OK I can rename BAM_MAX_DATA_SIZE to BAM_FIFO_SIZE, and use it when
setting BAM_P_FIFO_SIZES register. Is that fine to you?


-- 
regards,
Stan
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