linux-kernel - Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in __dma_device_satisfies

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Date:	Tue, 1 Dec 2015 11:47:29 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Vinod Koul <vinod.koul@...el.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Sekhar Nori <nsekhar@...com>,
	linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in
 __dma_device_satisfies_mask()

On 11/30/2015 04:35 PM, Andy Shevchenko wrote:
> On Mon, Nov 30, 2015 at 3:45 PM, Peter Ujfalusi <peter.ujfalusi@...com> wrote:
>> Treat as true condition the case when the mask is NULL.
> 
> What do you think about setting some default (all "on") mask when mask
> is not supplied?

Probably rephrasing the commit message to say that when the mask is NULL it
means that the caller does not care about the capabilities of the dma device
thus return with true in such a case.

We could also drop this patch and in private_candidate() :

-	if (!__dma_device_satisfies_mask(dev, mask)) {
+	if (mask && !__dma_device_satisfies_mask(dev, mask)) {
		pr_debug("%s: wrong capabilities\n", __func__);
		return NULL;
	}


> I don't know for sure but there might be cases when you don't want
> literally *any* channel to satisfy.

Or set DMA_SLAVE only in dma_request_chan()? What happens if we have cases
when we are able to request channel for memcpy via dma_request_chan()
(dedicated memcpy channel/DMA engine?) in that case we will have the SLAVE
set, but not MEMCPY, or any other variation we do not know yet?

>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
>> ---
>>  drivers/dma/dmaengine.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
>> index daf54a39bcc7..52c3eee48e2e 100644
>> --- a/drivers/dma/dmaengine.c
>> +++ b/drivers/dma/dmaengine.c
>> @@ -184,6 +184,9 @@ __dma_device_satisfies_mask(struct dma_device *device,
>>  {
>>         dma_cap_mask_t has;
>>
>> +       if (!want)
>> +               return true;
>> +
>>         bitmap_and(has.bits, want->bits, device->cap_mask.bits,
>>                 DMA_TX_TYPE_END);
>>         return bitmap_equal(want->bits, has.bits, DMA_TX_TYPE_END);
>> --
>> 2.6.3
>>
> 
> 
> 


-- 
Péter
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