[alsa-devel] [PATCH v5 06/10] dmaengine: add API for getting dma controller's quirk

Shawn Lin shawn.lin at rock-chips.com
Wed Oct 14 07:33:06 PDT 2015

On 2015/10/14 18:53, Vinod Koul wrote:
> On Thu, Oct 08, 2015 at 10:31:18AM +0200, Lars-Peter Clausen wrote:
>>> Basically I agree not to expose dma's quirk to slave controllers...But, the
>>> fact I mentioned on cover letter explain the reasons why I have to let slave
>>> controllers know that they are working with a broken dma. It's a dilemma
>>> that if we don't want that to be exposed(let slave controllers' driver get
>>> the info via a API), we have t add broken quirk for all of them ,here and
>>> there, which seems to be a disaster:(
>> The problem with this API is that it transports values with device specific
>> meanings over a generic API. Which is generally speaking not a good idea
>> because the consumer witch is supposed to be generic suddenly needs to know
>> which provider it is talking to.
>> A better solution in this case typically is either introduce a generic API
>> with generic values or a custom API with custom values, but don't mix the two.
>>> I would appreciate it if you could give me some suggestions at your earliest
>>> convenience. :)
>> In this case I think the best way to handle this is not quirks, but rather
>> expose the actual maximum burst size using the DMA capabilities API. Since
>> supporting only a certain burst depth is not really a quirk. All hardware
>> has a limit for this and for some it might be larger or smaller than for
>> others and it might be the same IP core but the maximum size depends on some
>> IP core parameters. So this should be discoverable.
> yes that makes more sense than adding quirks, exposing the right values
> which should be a readable property for driver will ensure it works on
> system with/without quirks

Sorry for late response in this thread.

Right, we can expose max-burst to clients by dma_slave_caps instead of 
quirks. I will try it and send v6 ASAP.

Thanks Lars and Vinod.


Best Regards
Shawn Lin

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