Messages in this thread | | | Subject | Re: [RFC/PATCH] media: omap3isp: Set maximum DMA segment size | From | Marek Szyprowski <> | Date | Tue, 17 Nov 2015 13:15:10 +0100 |
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Hi Laurent,
I really have no idea how this problem should be addressed. I've already proposed to handle it in videobuf2-dc, but this has been rejected. Maybe the only way will be to add dma_set_max_seg_size(isp->dev, DMA_BIT_MASK(32)) to every v4l2 driver, which use videobuf2-dc and add a check in videobuf2-dc.
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
On 2015-11-09 15:18, Laurent Pinchart wrote: > 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@ideasonboard.com> >> --- >> 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 */
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