From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>,
linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
robin.murphy@arm.com, robdclark@gmail.com,
linaro-kernel@lists.linaro.org,
stanislawski.tomasz@googlemail.com, daniel@ffwll.ch
Subject: Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms
Date: Wed, 11 Feb 2015 11:12:58 +0000 [thread overview]
Message-ID: <20150211111258.GP8656@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <54DB12B5.4080000@samsung.com>
On Wed, Feb 11, 2015 at 09:28:37AM +0100, Marek Szyprowski wrote:
> Hello,
>
> On 2015-01-27 09:25, Sumit Semwal wrote:
> >Add some helpers to share the constraints of devices while attaching
> >to the dmabuf buffer.
> >
> >At each attach, the constraints are calculated based on the following:
> >- max_segment_size, max_segment_count, segment_boundary_mask from
> > device_dma_parameters.
> >
> >In case the attaching device's constraints don't match up, attach() fails.
> >
> >At detach, the constraints are recalculated based on the remaining
> >attached devices.
> >
> >Two helpers are added:
> >- dma_buf_get_constraints - which gives the current constraints as calculated
> > during each attach on the buffer till the time,
> >- dma_buf_recalc_constraints - which recalculates the constraints for all
> > currently attached devices for the 'paranoid' ones amongst us.
> >
> >The idea of this patch is largely taken from Rob Clark's RFC at
> >https://lkml.org/lkml/2012/7/19/285, and the comments received on it.
> >
> >Cc: Rob Clark <robdclark@gmail.com>
> >Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
>
> The code looks okay, although it will probably will work well only with
> typical cases like 'contiguous memory needed' or 'no constraints at all'
> (iommu).
Which is a damn good reason to NAK it - by that admission, it's a half-baked
idea.
If all we want to know is whether the importer can accept only contiguous
memory or not, make a flag to do that, and allow the exporter to test this
flag. Don't over-engineer this to make it _seem_ like it can do something
that it actually totally fails with.
As I've already pointed out, there's a major problem if you have already
had a less restrictive attachment which has an active mapping, and a new
more restrictive attachment comes along later.
It seems from Rob's descriptions that we also need another flag in the
importer to indicate whether it wants to have a valid struct page in the
scatter list, or whether it (correctly) uses the DMA accessors on the
scatter list - so that exporters can reject importers which are buggy.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
next prev parent reply other threads:[~2015-02-11 11:13 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-27 8:25 [RFCv3 1/2] device: add dma_params->max_segment_count Sumit Semwal
2015-01-27 8:25 ` [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Sumit Semwal
2015-01-29 14:16 ` Maarten Lankhorst
2015-01-29 14:39 ` Russell King - ARM Linux
2015-01-29 15:30 ` Sumit Semwal
2015-01-29 15:47 ` Russell King - ARM Linux
2015-01-29 16:55 ` Sumit Semwal
2015-01-29 18:52 ` Rob Clark
2015-01-29 19:26 ` Russell King - ARM Linux
2015-01-29 22:18 ` Rob Clark
2015-01-29 22:31 ` Russell King - ARM Linux
2015-01-29 23:19 ` Rob Clark
2015-02-02 16:54 ` Daniel Vetter
2015-02-02 20:30 ` Rob Clark
2015-02-02 21:46 ` Russell King - ARM Linux
2015-02-02 22:36 ` Rob Clark
2015-02-03 7:50 ` Daniel Vetter
2015-02-03 7:46 ` Daniel Vetter
2015-02-03 7:48 ` Daniel Vetter
2015-02-03 12:28 ` Russell King - ARM Linux
2015-02-03 13:00 ` Daniel Vetter
2015-02-03 13:28 ` Christian Gmeiner
2015-02-03 14:32 ` Russell King - ARM Linux
2015-02-03 14:25 ` Rob Clark
2015-02-03 14:04 ` Rob Clark
2015-02-03 14:17 ` Arnd Bergmann
2015-02-03 14:41 ` Russell King - ARM Linux
2015-02-03 14:52 ` Arnd Bergmann
2015-02-03 15:22 ` Russell King - ARM Linux
2015-02-03 15:31 ` [Linaro-mm-sig] " Arnd Bergmann
2015-02-03 15:54 ` Russell King - ARM Linux
2015-02-03 16:12 ` Arnd Bergmann
2015-02-03 16:22 ` Rob Clark
2015-02-03 16:36 ` Arnd Bergmann
2015-02-03 20:04 ` Daniel Vetter
2015-02-03 21:42 ` Arnd Bergmann
2015-02-03 22:07 ` Daniel Vetter
2015-02-04 0:14 ` Russell King - ARM Linux
2015-02-03 17:01 ` Russell King - ARM Linux
2015-02-03 16:58 ` Russell King - ARM Linux
2015-02-03 17:35 ` Rob Clark
2015-02-03 20:08 ` Daniel Vetter
2015-02-03 21:44 ` Arnd Bergmann
2015-02-03 15:25 ` Rob Clark
2015-02-03 15:19 ` Rob Clark
2015-02-03 14:37 ` Russell King - ARM Linux
2015-02-03 14:44 ` Rob Clark
2015-02-03 14:58 ` Russell King - ARM Linux
2015-02-02 5:53 ` Sumit Semwal
2015-02-11 8:28 ` Marek Szyprowski
2015-02-11 11:12 ` Russell King - ARM Linux [this message]
2015-02-11 11:23 ` Rob Clark
2015-02-11 12:56 ` Daniel Vetter
2015-02-11 13:30 ` Rob Clark
2015-02-11 12:20 ` Marek Szyprowski
2015-02-11 16:23 ` Russell King - ARM Linux
2015-05-05 14:41 ` Sumit Semwal
2015-06-03 6:39 ` [Linaro-mm-sig] " Hans Verkuil
2015-06-03 8:41 ` Russell King - ARM Linux
2015-06-03 9:37 ` Hans Verkuil
2015-06-04 5:24 ` Sumit Semwal
2015-01-28 14:09 ` [RFCv3 1/2] device: add dma_params->max_segment_count Marek Szyprowski
2015-06-03 6:13 ` [Linaro-mm-sig] " Hans Verkuil
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