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

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Date:   Tue, 14 Feb 2017 09:24:35 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        dmaengine@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Arnd Bergmann <arnd@...db.de>, Inki Dae <inki.dae@...sung.com>
Subject: Re: [PATCH v8 3/3] dmaengine: pl330: Don't require irq-safe runtime PM

On 13 February 2017 at 16:47, Vinod Koul <vinod.koul@...el.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