Hi Marek, Thanks for the patch! On Thu, Apr 28, 2016 at 03:20:03PM +0200, Marek Szyprowski wrote: > 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> > --- > 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: > 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 | 39 ++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) > > diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c > index 461ae55eaa98..d0382d62954d 100644 > --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c > +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c > @@ -443,6 +443,36 @@ 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 > + * scatter-list 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. > + */ > +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); Doesn't this create a memory leak? Do consider that devices may be also removed from the system at runtime. Looks very nice otherwise. > + if (!dev->dma_parms) > + return -ENOMEM; > + } > + if (dma_get_max_seg_size(dev) < size) > + return dma_set_max_seg_size(dev, size); > + > + return 0; > +} > + > +/* > * For some kind of reserved memory there might be no struct page available, > * so all that can be done to support such 'pages' is to try to convert > * pfn to dma address or at the last resort just assume that > @@ -499,6 +529,10 @@ static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr, > return ERR_PTR(-EINVAL); > } > > + ret = vb2_dc_set_max_seg_size(dev, PAGE_ALIGN(size + PAGE_SIZE)); > + if (!ret) > + return ERR_PTR(ret); > + > buf = kzalloc(sizeof *buf, GFP_KERNEL); > if (!buf) > return ERR_PTR(-ENOMEM); > @@ -675,10 +709,15 @@ static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf, > { > struct vb2_dc_buf *buf; > struct dma_buf_attachment *dba; > + int ret; > > if (dbuf->size < size) > return ERR_PTR(-EFAULT); > > + ret = vb2_dc_set_max_seg_size(dev, PAGE_ALIGN(size)); > + if (!ret) > + return ERR_PTR(ret); > + > buf = kzalloc(sizeof(*buf), GFP_KERNEL); > if (!buf) > return ERR_PTR(-ENOMEM); -- Kind regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx -- 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
