Re: [PATCH v8 3/3] dmaengine: pl330: Don't require irq-safe runtime PM

Ulf Hansson
2017-02-14T08:24:40Z

On 13 February 2017 at 16:47, Vinod Koul <vinod.koul@intel.com> wrote:
> On Mon, Feb 13, 2017 at 04:32:32PM +0100, Ulf Hansson wrote:
>> [...]
>>
>> >> Although, I don't know of other examples, besides the runtime PM use
>> >> case, where non-atomic channel prepare/unprepare would make sense. Do
>> >> you?
>> >
>> > The primary ask for that has been to enable runtime_pm for drivers. It's not
>> > a new ask, but we somehow haven't gotten around to do it.
>>
>> Okay, I see.
>>
>> >
>> >> > As I said earlier, if we want to solve that problem a better idea is to
>> >> > actually split the prepare as we discussed in [1]
>> >> >
>> >> > This way we can get a non atomic descriptor allocate/prepare and release.
>> >> > Yes we need to redesign the APIs to solve this, but if you guys are up for
>> >> > it, I think we can do it and avoid any further round abouts :)
>> >>
>> >> Adding/re-designing dma APIs is a viable option to solve the runtime PM case.
>> >>
>> >> Changes would be needed for all related dma client drivers as well,
>> >> although if that's what we need to do - let's do it.
>> >
>> > Yes, but do bear in mind that some cases do need atomic prepare. The primary
>> > cases for DMA had that in mind and also submitting next transaction from the
>> > callback (tasklet) context, so that won't go away.
>> >
>> > It would help in other cases where clients know that they will not be in
>> > atomic context so we provide additional non-atomic "allocation" followed by
>> > prepare, so that drivers can split the work among these and people can do
>> > runtime_pm and other things..
>>
>> That for sharing the details.
>>
>> It seems like some dma expert really need to be heavily involved if we
>> ever are going to complete this work. :-)
>
> Sure, I will help out :)

That sounds great! :-)

>
> If anyone of you are in Portland next week, then we can discuss these f2f. I
> will try taking a stab at the new API design next week.
>

Unfortunate not. We will have to meet some other time. Anyway, please
keep me posted on any related topics.

Kind regards
Uffe