linux-kernel - Re: [PATCH v2] dmaengine: xgene-dma: Disable memcpy operation due to performance drop

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Date:	Fri, 9 Oct 2015 22:08:32 +0530
From:	Rameshwar Sahu <rsahu@....com>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	dan.j.williams@...el.com, dmaengine@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	jcm@...hat.com, patches@....com
Subject: Re: [PATCH v2] dmaengine: xgene-dma: Disable memcpy operation due to
 performance drop

Hi Vinod,

On Fri, Oct 9, 2015 at 9:42 PM, Vinod Koul <vinod.koul@...el.com> wrote:
> On Thu, Oct 08, 2015 at 02:36:57PM +0530, Rameshwar Prasad Sahu wrote:
>> The DMA engine supports memory copy, RAID5 XOR, RAID6 PQ, and other
>> computations. But the bandwidth of the entire DMA engine is shared
>> among all channels. This patch re-configures operations availability
>> such that one can achieve maximum performance for XOR and PQ
>> computation by removing the memory offload operations.
>>
>> Signed-off-by: Rameshwar Prasad Sahu <rsahu@....com>
>> ---
>>  drivers/dma/xgene-dma.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/dma/xgene-dma.c b/drivers/dma/xgene-dma.c
>> index 8d57b1b..cd38022 100644
>> --- a/drivers/dma/xgene-dma.c
>> +++ b/drivers/dma/xgene-dma.c
>> @@ -1707,7 +1707,6 @@ static void xgene_dma_set_caps(struct xgene_dma_chan *chan,
>>       dma_cap_zero(dma_dev->cap_mask);
>>
>>       /* Set DMA device capability */
>> -     dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
>>       dma_cap_set(DMA_SG, dma_dev->cap_mask);
>
> This will not work. Still clients can invoke memcpy operation. You need to
> remove the callback

Got it, instead of removing the callback registration can we keep it
inside the condition like..

if (dma_has_cap(DMA_MEMCPY, dma_dev->cap_mask))
            dma_dev->device_prep_dma_memcpy = xgene_dma_prep_memcpy;


>
> --
> ~Vinod
--
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