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. 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! Regards, Mauro -- Thanks, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
