On Fri, Dec 23, 2016 at 11:38:19AM +0100, Marek Szyprowski wrote:
(...)
> >>The main assumption for it is an
> >>observation that there can be only one slave device using each DMA channel.
> >Wait, observation, real requirement or assumption?
> >
> >Later in the code I see adding such requirement.
>
> Well, observation which result in assumption. I cannot imagine a hardware
> which
> shares slave DMA channel between devices. Also none of the existing platform
> does it.
OK for me.
>
> >>Using recently introduced device dependencies (links) infrastructure one can
> >>ensure proper runtime PM state of PL330 DMA controller. In this approach in
> >>pl330_alloc_chan_resources() function a new dependency is being created
> >>between PL330 DMA controller device (as supplier) and given slave device
> >>(as consumer). This way PL330 DMA controller device runtime active counter
> >>is increased when the slave device is resumed and decreased the same time
> >>when given slave device is put to suspend. This way it has been ensured to
> >>keep PL330 DMA controller runtime active if there is an active used of any
> >>of its DMA channels. Slave device pointer is initially stored in per-channel
> >>data in of_dma_xlate callback. This is similar to what has been already
> >>implemented in Exynos IOMMU driver in commit 2f5f44f205cc958b
> >>("iommu/exynos: Use device dependency links to control runtime pm").
> >Sounds convincing... Interesting approach!
> >
> >My doubts are:
> >1. What with more then one slave device? (assumption?)
>
> See above, there are no such cases.
>
> >2. If slave device does not implement runtime PM, then pl330 will be
> > active all the time?
>
> Right, but the goal is to have runtime pm added to all devices in the
> system.
>
> >3. If slave device implements runtime PM in a way that it's enabled in
> > probe and released in remove, then pl330 will be active all the time?
>
> Then it will force power domain to be turned on all the time and even
> optional
> fine-grained irq-safe runtiem pm in pl330 driver won't help much to reduce
> power
> consumption. I assume that the real goal with runtime pm is to let
> respective
> power domains to be turned off, what gives the best results in terms of
> power
> saving.
Indeed existing runtime PM for pl330 was not bringing much benefits of
its own - only clocks were enabled/disabled.
Thanks for clarifications.
(...)
> >>@@ -2113,14 +2089,63 @@ static struct dma_chan *of_dma_pl330_xlate(struct of_phandle_args *dma_spec,
> >> if (chan_id >= pl330->num_peripherals)
> >> return NULL;
> >>+ if (!pl330->peripherals[chan_id].slave)
> >>+ pl330->peripherals[chan_id].slave = slave;
> >>+ else if (pl330->peripherals[chan_id].slave != slave) {
> >>+ dev_err(pl330->ddma.dev,
> >>+ "Can't use same channel with multiple slave devices!\n");
> >>+ return NULL;
> >>+ }
> >This could be nicely split into separate patch.
>
> Okay, if you want, I can move this change to separate patch.
Yes, please do it. Beside that patch looked fine to me.
Best regards,
Krzysztof
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