From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Vinod Koul <vinod.koul@intel.com>,
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>,
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: Wed, 05 Nov 2014 16:54:33 +0200 [thread overview]
Message-ID: <22827785.xmOLWzI5M2@avalon> (raw)
In-Reply-To: <20141103170408.GD4042@n2100.arm.linux.org.uk>
Hi Russell,
On Monday 03 November 2014 17:04:08 Russell King - ARM Linux wrote:
> On Mon, Nov 03, 2014 at 09:57:28PM +0530, Vinod Koul wrote:
> > On Sat, Nov 01, 2014 at 02:29:42AM +0200, Laurent Pinchart wrote:
> >> 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.
>
> Except we /do/ have a fair number of places where the prep calls are made
> from atomic contexts, particularly in serial drivers. You'd need to
> introduce a tasklet into almost every serial driver which doesn't
> already have one to restart RX DMA after an error or pause. Eg,
>
> drivers/tty/serial/amba-pl011.c
> drivers/tty/serial/pch_uart.c
> drivers/tty/serial/imx.c
I wonder whether it would be possible to decouple descriptor allocation and
descriptor initialization/preparation. If drivers could allocate descriptors
and reuse them after they complete, not only would it lower the memory
management pressure by getting rid of alloc/free during transmission, but it
would also make it possible to easily allocate the transaction descriptors
beforehand in non-atomic context.
> Probably also:
>
> drivers/net/ethernet/micrel/ks8842.c
>
> There could well be other places as well, I've not gone through and
> checked exhaustively.
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2014-11-05 17:59 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
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 [this message]
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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