Re: [PATCH 02/15] ARM: pxa: add dma slave map

From: Robert Jarzmik
Date: Wed Apr 04 2018 - 15:22:32 EST

Arnd Bergmann <arnd@xxxxxxxx> writes:

> On Tue, Apr 3, 2018 at 10:19 PM, Robert Jarzmik <robert.jarzmik@xxxxxxx> wrote:
>> ... chop chop removing unneeded recipients ....
>> Arnd Bergmann <arnd@xxxxxxxx> writes:
>>> It still feels odd to me that there is an entry in the slave map for
>>> a device that does not have a request line. However, it also seems
>>> that the entire code in those two drivers that deals with DMA is specific
>>> to PXA anyway, so maybe it can be done differently: instead of
>>> calling dma_request_slave_channel_compat() or dma_request_chan()
>>> with a fake request line, how about calling dma_request_channel()
>>> with an NULL filter function and data, and have the driver handle
>>> the empty data case the same way as the rq=-1 case today?
>> Okay, in this case :
>> - the channel priority cannot be passed anymore
> Right, but it could just always use a static priority, right?
Yes, an implicit default priority. I'm not a big fan of implicit parameters, yet
I can do it.

>> - and I don't see how this can work :
>> dma_request_channel()
>> __dma_request_channel()
>> find_candidate()
>> private_candidate(mask, device, fn, fn_param);
>> /* Here, fn == NULL and fn_param == NULL as per your proposal */
>> This function will find the first available dma channel, all right, but
>> no function will be called in pxa_dma driver, and therefore the last
>> requestor of the channel will be used, which is bad.
> Can't you just reset those in pxad_free_chan_resources()?
I can, let's see what happens next ...