Hello everybody, Ping ? On Tuesday 13 October 2015 16:18:36 Laurent Pinchart wrote: > The maximum DMA segment size controls the IOMMU mapping granularity. Its > default value is 64kB, resulting in potentially non-contiguous IOMMU > mappings. Configure it to 4GB to ensure that buffers get mapped > contiguously. > > Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > --- > drivers/media/platform/omap3isp/isp.c | 4 ++++ > drivers/media/platform/omap3isp/isp.h | 1 + > 2 files changed, 5 insertions(+) > > I'm posting this as an RFC because I'm not happy with the patch, even if it > gets the job done. > > On ARM the maximum DMA segment size is used when creating IOMMU mappings. As > a large number of devices require contiguous memory buffers (this is a very > common requirement for video-related embedded devices) the default 64kB > value doesn't work. > > I haven't investigated the history behind this API in details but I have a > feeling something is not quite right. We force most drivers to explicitly > set the maximum segment size from a default that seems valid for specific > use cases only. Furthermore, as the DMA parameters are not stored directly > in struct device this require allocation of external memory for which we > have no proper management rule, making automatic handling of the DMA > parameters in frameworks or helper functions cumbersome (for a discussion > on this topic see http://www.spinics.net/lists/linux-media/msg92467.html > and http://lists.infradead.org/pipermail/linux-arm-kernel/2014-> November/305913.html). > > Is it time to fix this mess ? > > diff --git a/drivers/media/platform/omap3isp/isp.c > b/drivers/media/platform/omap3isp/isp.c index 17430a6ed85a..ebf7dc76e94d > 100644 > --- a/drivers/media/platform/omap3isp/isp.c > +++ b/drivers/media/platform/omap3isp/isp.c > @@ -2444,6 +2444,10 @@ static int isp_probe(struct platform_device *pdev) > if (ret) > goto error; > > + isp->dev->dma_parms = &isp->dma_parms; > + dma_set_max_seg_size(isp->dev, DMA_BIT_MASK(32)); > + dma_set_seg_boundary(isp->dev, 0xffffffff); > + > platform_set_drvdata(pdev, isp); > > /* Regulators */ > diff --git a/drivers/media/platform/omap3isp/isp.h > b/drivers/media/platform/omap3isp/isp.h index e579943175c4..4b2231cf01be > 100644 > --- a/drivers/media/platform/omap3isp/isp.h > +++ b/drivers/media/platform/omap3isp/isp.h > @@ -193,6 +193,7 @@ struct isp_device { > u32 syscon_offset; > u32 phy_type; > > + struct device_dma_parameters dma_parms; > struct dma_iommu_mapping *mapping; > > /* ISP Obj */ -- Regards, Laurent Pinchart -- 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
