On Sat, Nov 01, 2014 at 02:29:42AM +0200, Laurent Pinchart wrote: > Hi Krzysztof, > > On Friday 31 October 2014 15:40:16 Krzysztof Kozlowski wrote: > > On pią, 2014-10-31 at 15:22 +0100, Pavel Machek wrote: > > > On Fri 2014-10-31 10:14:55, Krzysztof Kozlowski wrote: > > >> On pon, 2014-10-20 at 11:04 +0200, Krzysztof Kozlowski wrote: > > >>> Add a simple getter pm_runtime_is_irq_safe() for querying whether > > >>> runtime PM IRQ safe was set or not. > > >>> > > >>> Various bus drivers implementing runtime PM may use choose to suspend > > >>> differently based on IRQ safeness status of child driver (e.g. do not > > >>> unprepare the clock if IRQ safe is not set). > > >>> > > >>> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> > > >>> Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > > >> > > >> Rafael, Len, Pavel, > > >> > > >> Is proposed API ok? Do you have any comments? > > >> > > >> I'll upload whole patchset to Russell's patch tracking system. However > > >> an ack from PM maintainer is probably needed. > > > > > > I don't like the API. Having callbacks work in different context (irq > > > / noirq) based on what another function reports is ugly. > > > > > > What is the penalty if we always decide callbacks are not IRQ safe? > > > > Then pm_runtime_get_sync() could not be called in atomic context. The > > pl330 runtime PM would have to be completely reworked because one > > pm_runtime_get_sync() is called in device_issue_pending which cannot > > sleep (at least in non preemptible kernels). Probably this can be solved > > some way... > > Many other drivers suffer from the same problem. While I won't reject your > proposed fix, I would prefer a more generic approach. > > One option that has been discussed previously was to use a work queue to delay > starting the DMA transfer to an interruptible context where > pm_runtime_get_sync() could be called. However, as Russell pointed out [1], > even that won't work in all cases as the DMA slave might need the transfer to > be started before enabling part of its hardware (OMAP audio seem to be such a > case). > > I've heard a rumor of a possible DMA engine rework to forbid calling the > descriptor preparation API from atomic context. This could be used as a base > to implement runtime PM, as DMA slave drivers should not prepare descriptors > if they don't need to use them. However that's a long term plan, and we need a > solution sooner than that. Well it is not a rumour :) I have been contemplating that now that async_tx will be killed so we dont have to worry about that usage. For the slave dma usage, we can change the prepare API to be non atomic. I think the users will be okay with approach. This way drivers can use runtime pm calls in prepare. -- ~Vinod > > I've been toying with the idea of adding explicit open/close (or whatever we > would call them) operations to the DMA engine API. Those would be used by DMA > slave drivers to signal that they will start/stop using the DMA engine. > > If (1) we must start the DMA synchronously with a DMA slave call, (2) need to > sleep to handle PM, and (3) don't want to keep the DMA engine powered for as > long as one channel is requested, then we need to turn at least preparation as > not callable in atomic context, or introduce a new operation. > > [1] http://www.spinics.net/lists/dmaengine/msg01548.html > > > >>> --- a/Documentation/power/runtime_pm.txt > > >>> +++ b/Documentation/power/runtime_pm.txt > > >>> > > >>> @@ -468,6 +468,10 @@ drivers/base/power/runtime.c and > > >>> include/linux/pm_runtime.h: > > >>> - set the power.irq_safe flag for the device, causing the > > >>> runtime-PM > > >>> > > >>> callbacks to be invoked with interrupts off > > >>> > > >>> + bool pm_runtime_is_irq_safe(struct device *dev); > > >>> + - return true if power.irq_safe flag was set for the device, > > >>> causing > > >>> + the runtime-PM callbacks to be invoked with interrupts off > > >>> + > > >>> > > >>> void pm_runtime_mark_last_busy(struct device *dev); > > >>> > > >>> - set the power.last_busy field to the current time > > -- > Regards, > > Laurent Pinchart > -- -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
