Hi Mauro
On 2016-05-06 20:52, Mauro Carvalho Chehab wrote:
Em Wed, 04 May 2016 11:00:03 +0200
Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> escreveu:
This patch lets vb2-dma-contig memory allocator to configure DMA max
segment size properly for the client device. Setting it is needed to let
DMA-mapping subsystem to create a single, contiguous mapping in DMA
address space. This is essential for all devices, which use dma-contig
videobuf2 memory allocator and shared buffers (in USERPTR or DMAbuf modes
of operations).
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
Hello,
This patch is a follow-up of my previous attempts to let Exynos
multimedia devices to work properly with shared buffers when IOMMU is
enabled:
1. https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg96946.html
2. http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/97316
3. https://patchwork.linuxtv.org/patch/30870/
As sugested by Hans, configuring DMA max segment size should be done by
videobuf2-dma-contig module instead of requiring all device drivers to
do it on their own.
Here is some backgroud why this is done in videobuf2-dc not in the
respective generic bus code:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/305913.html
Best regards,
Marek Szyprowski
changelog:
v4:
- rebased onto media master tree
- call vb2_dc_set_max_seg_size after allocating vb2 buf object
v3:
- added FIXME note about possible memory leak
v2:
- fixes typos and other language issues in the comments
v1: http://article.gmane.org/gmane.linux.kernel.samsung-soc/53690
---
drivers/media/v4l2-core/videobuf2-dma-contig.c | 53 +++++++++++++++++++++++++-
1 file changed, 51 insertions(+), 2 deletions(-)
diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index 5361197f3e57..6291842a889f 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -448,6 +448,42 @@ static void vb2_dc_put_userptr(void *buf_priv)
}
/*
+ * To allow mapping the scatter-list into a single chunk in the DMA
+ * address space, the device is required to have the DMA max segment
+ * size parameter set to a value larger than the buffer size. Otherwise,
+ * the DMA-mapping subsystem will split the mapping into max segment
+ * size chunks. This function increases the DMA max segment size
+ * parameter to let DMA-mapping map a buffer as a single chunk in DMA
+ * address space.
+ * This code assumes that the DMA-mapping subsystem will merge all
+ * scatterlist segments if this is really possible (for example when
+ * an IOMMU is available and enabled).
+ * Ideally, this parameter should be set by the generic bus code, but it
+ * is left with the default 64KiB value due to historical litmiations in
+ * other subsystems (like limited USB host drivers) and there no good
+ * place to set it to the proper value. It is done here to avoid fixing
+ * all the vb2-dc client drivers.
+ *
+ * FIXME: the allocated dma_params structure is leaked because there
+ * is completely no way to determine when to free it (dma_params might have
+ * been also already allocated by the bus code). However in typical
+ * use cases this function will be called for platform devices, which are
+ * not hot-plugged and exist all the time in the target system.
+ */
+static int vb2_dc_set_max_seg_size(struct device *dev, unsigned int size)
+{
+ if (!dev->dma_parms) {
+ dev->dma_parms = kzalloc(sizeof(dev->dma_parms), GFP_KERNEL);
Why don't you use devm_kzalloc() here? dma_parms will then be freed
if the device gets hot-unplugged/unbind.
Although the structure will be freed, but the pointer in the struct device
will still point to the freed resource. Please note that devm_ allocations
are freed on driver removal/unbind not on device removal. That's why I
decided
to leak memory instead of allowing to access resource that has been freed.
And yes: it is possible to hot-unplug (actually, hot-unbind) a platform
device via sysfs.
Just assuming that only platform drivers will use dma-contig and adding
a memory leak here seems really ugly!
The whole handling of dma_params structure is really ugly and right now
there
is no good way of ensuring proper dma parameters.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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