linux-kernel - Re: [PATCH] ata: pata_arasam_cf: Use dma_request_chan() instead dma_request_slave

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Date:   Mon, 13 Jan 2020 16:33:01 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
CC:     Viresh Kumar <viresh.kumar@...aro.org>, <vireshk@...nel.org>,
        <axboe@...nel.dk>, <vkoul@...nel.org>, <linux-ide@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ata: pata_arasam_cf: Use dma_request_chan() instead
 dma_request_slave_channel()



On 13/01/2020 13.31, Bartlomiej Zolnierkiewicz wrote:
> 
> On 12/17/19 12:19 PM, Viresh Kumar wrote:
>> On 17-12-19, 12:50, Peter Ujfalusi wrote:
>>> dma_request_slave_channel() is a wrapper on top of dma_request_chan()
>>> eating up the error code.
>>>
>>> By using dma_request_chan() directly the driver can support deferred
>>> probing against DMA.
> 
> It doesn't seem to be the case as DMA channel is requested at the start
> of the data transfer (which happens after the driver has been successfully
> probed).

True, I have updated the commit message to remove the reference to
deferred probing.
If the DMA is requested upfront (at probe time, device open time?) the
driver would save quite a bit of time by not allocating and freeing the
DMA resources repeatedly for each transfer, thus most likely giving a
boost to throughput...

> PS there is a typo in the patch summary (it should "pata_arasan_cf").

Ah, fixed this as well in v2.

Thanks for catching them,
- Péter

> 
> Best regards,
> --
> Bartlomiej Zolnierkiewicz
> Samsung R&D Institute Poland
> Samsung Electronics
> 
>>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
>>> ---
>>>  drivers/ata/pata_arasan_cf.c | 6 ++++--
>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/ata/pata_arasan_cf.c b/drivers/ata/pata_arasan_cf.c
>>> index 135173c8d138..69b555d83f68 100644
>>> --- a/drivers/ata/pata_arasan_cf.c
>>> +++ b/drivers/ata/pata_arasan_cf.c
>>> @@ -526,9 +526,10 @@ static void data_xfer(struct work_struct *work)
>>>  
>>>  	/* request dma channels */
>>>  	/* dma_request_channel may sleep, so calling from process context */
>>> -	acdev->dma_chan = dma_request_slave_channel(acdev->host->dev, "data");
>>> -	if (!acdev->dma_chan) {
>>> +	acdev->dma_chan = dma_request_chan(acdev->host->dev, "data");
>>> +	if (IS_ERR(acdev->dma_chan)) {
>>>  		dev_err(acdev->host->dev, "Unable to get dma_chan\n");
>>> +		acdev->dma_chan = NULL;
>>>  		goto chan_request_fail;
>>>  	}
>>>  
>>> @@ -539,6 +540,7 @@ static void data_xfer(struct work_struct *work)
>>>  	}
>>>  
>>>  	dma_release_channel(acdev->dma_chan);
>>> +	acdev->dma_chan = NULL;
>>>  
>>>  	/* data xferred successfully */
>>>  	if (!ret) {
>>
>> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
>>
> 

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