From: Vinod Koul <vinod.koul@intel.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>,
Pavel Machek <pavel@ucw.cz>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Len Brown <len.brown@intel.com>, Jonathan Corbet <corbet@lwn.net>,
Russell King <linux@arm.linux.org.uk>,
Dan Williams <dan.j.williams@intel.com>,
Ulf Hansson <ulf.hansson@linaro.org>,
Alan Stern <stern@rowland.harvard.edu>,
linux-pm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
Lars-Peter Clausen <lars@metafoo.de>,
Michal Simek <michal.simek@xilinx.com>,
Kyungmin Park <kyungmin.park@samsung.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option
Date: Mon, 3 Nov 2014 21:57:28 +0530 [thread overview]
Message-ID: <20141103162728.GB1870@intel.com> (raw)
In-Reply-To: <3452823.YQ5FR2FtKz@avalon>
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@samsung.com>
> > >>> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
> > >>
> > >> 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
>
--
next prev parent reply other threads:[~2014-11-03 16:27 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-20 9:04 [PATCH v8 0/5] amba/dma: pl330: add Power Management support Krzysztof Kozlowski
2014-10-20 9:04 ` [PATCH v8 1/5] PM / Runtime: Add getter for querying the IRQ safe option Krzysztof Kozlowski
2014-10-31 9:14 ` Krzysztof Kozlowski
2014-10-31 9:29 ` Ulf Hansson
2014-10-31 9:33 ` Russell King - ARM Linux
2014-10-31 9:54 ` Ulf Hansson
2014-10-31 9:33 ` Krzysztof Kozlowski
2014-10-31 14:22 ` Pavel Machek
2014-10-31 14:40 ` Krzysztof Kozlowski
2014-11-01 0:29 ` Laurent Pinchart
2014-11-03 9:36 ` Krzysztof Kozlowski
2014-11-03 16:27 ` Vinod Koul [this message]
2014-11-03 16:59 ` Laurent Pinchart
2014-11-05 14:09 ` Vinod Koul
2014-11-03 17:04 ` Russell King - ARM Linux
2014-11-05 14:04 ` Vinod Koul
2014-11-05 14:54 ` Laurent Pinchart
2014-10-31 23:11 ` Rafael J. Wysocki
2014-10-31 23:04 ` Russell King - ARM Linux
2014-11-01 0:42 ` Rafael J. Wysocki
2014-11-03 8:51 ` Krzysztof Kozlowski
2014-10-20 9:04 ` [PATCH v8 2/5] amba: Add helpers for (un)preparing AMBA clock Krzysztof Kozlowski
2014-10-21 8:05 ` Ulf Hansson
2014-10-20 9:04 ` [PATCH v8 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM Krzysztof Kozlowski
2014-11-01 0:45 ` Rafael J. Wysocki
2014-11-01 0:55 ` Russell King - ARM Linux
2014-11-01 1:01 ` Russell King - ARM Linux
2014-11-03 8:36 ` Krzysztof Kozlowski
2014-11-03 10:04 ` Russell King - ARM Linux
2014-11-03 15:41 ` Alan Stern
2014-11-03 15:44 ` Russell King - ARM Linux
2014-11-04 7:59 ` Krzysztof Kozlowski
2014-11-04 1:57 ` Rafael J. Wysocki
2014-11-04 8:01 ` Krzysztof Kozlowski
2014-11-04 9:11 ` Ulf Hansson
2014-11-04 13:59 ` Rafael J. Wysocki
2014-11-04 16:19 ` Ulf Hansson
2014-11-03 17:17 ` Kevin Hilman
2014-10-20 9:04 ` [PATCH v8 4/5] dma: pl330: add Power Management support Krzysztof Kozlowski
2014-10-20 9:04 ` [PATCH v8 5/5] amba: Remove unused amba_pclk_enable/disable macros Krzysztof Kozlowski
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