Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in __dma_device_satisfies_mask()

From	Andy Shevchenko <andy.shevchenko@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in __dma_device_satisfies_mask()
Date	2015-12-01 14:00 +0100
Message-ID	<qASHg-1kx-13@gated-at.bofh.it> (permalink)
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On Tue, Dec 1, 2015 at 11:47 AM, Peter Ujfalusi <peter.ujfalusi@ti.com> wrote:
> On 11/30/2015 04:35 PM, Andy Shevchenko wrote:
>> On Mon, Nov 30, 2015 at 3:45 PM, Peter Ujfalusi <peter.ujfalusi@ti.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;
>         }

Between patch and above proposal I would choose the latter one.

>> 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?

Frankly, have no idea.

-- 
With Best Regards,
Andy Shevchenko
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Thread

Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in  __dma_device_satisfies_mask() Peter Ujfalusi <peter.ujfalusi@ti.com> - 2015-12-01 10:50 +0100
  Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in __dma_device_satisfies_mask() Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-12-01 14:00 +0100
    Re: [RFC v02 01/15] dmaengine: core: Allow NULL mask pointer in  __dma_device_satisfies_mask() Vinod Koul <vinod.koul@intel.com> - 2015-12-01 18:10 +0100

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