Hello, On Tuesday, 15 May 2018 10:30:28 EEST Fabien DESSENNE wrote: > On 14/05/18 12:39, Mauro Carvalho Chehab wrote: > > Em Mon, 14 May 2018 07:35:03 -0300 Mauro Carvalho Chehab escreveu: > >> Em Mon, 14 May 2018 08:00:37 +0000 Fabien DESSENNE escreveu: > >>> On 07/05/18 17:19, Mauro Carvalho Chehab wrote: > >>>> Em Mon, 07 May 2018 16:26:08 +0300 Laurent Pinchart escreveu: > >>>>> On Saturday, 5 May 2018 19:08:15 EEST Mauro Carvalho Chehab wrote: > >>>>> > >>>>>> There was a recent discussion about the use/abuse of GFP_DMA flag > >>>>>> when allocating memories at LSF/MM 2018 (see Luis notes enclosed). > >>>>>> > >>>>>> The idea seems to be to remove it, using CMA instead. Before doing > >>>>>> that, better to check if what we have on media is are valid use cases > >>>>>> for it, or if it is there just due to some misunderstanding (or > >>>>>> because it was copied from some other code). > >>>>>> > >>>>>> Hans de Goede sent us today a patch stopping abuse at gspca, and I'm > >>>>>> also posting today two other patches meant to stop abuse of it on > >>>>>> USB drivers. Still, there are 4 platform drivers using it: > >>>>>> > >>>>>> $ git grep -l -E "GFP_DMA\\b" drivers/media/ > >>>>>> drivers/media/platform/omap3isp/ispstat.c > >>>>>> drivers/media/platform/sti/bdisp/bdisp-hw.c > >>>>>> drivers/media/platform/sti/hva/hva-mem.c > >>> > >>> The two STI drivers (bdisp-hw.c and hva-mem.c) are only expected to run > >>> on ARM platforms, not on x86. Since this thread deals with x86 & DMA > >>> trouble, I am not sure that we actually have a problem for the sti > >>> drivers. > >>> > >>> There are some other sti drivers that make use of this GFP_DMA flag > >>> (drivers/gpu/drm/sti/sti_*.c) and it does not seem to be a problem. > >>> > >>> Nevertheless I can see that the media sti drivers depend on COMPILE_TEST > >>> (which is not the case for the DRM ones). > >>> Would it be an acceptable solution to remove the COMPILE_TEST > >>> dependency? > >> > >> This has nothing to do with either x86 or COMPILE_TEST. The thing is > >> that there's a plan for removing GFP_DMA from the Kernel[1], as it was > >> originally meant to be used only by old PCs, where the DMA controllers > >> used only on the bottom 16 MB memory address (24 bits). IMHO, it is > >> very unlikely that any ARM SoC have such limitation. > >> > >> [1] https://lwn.net/Articles/753273/ (article will be freely available > >> on May, 17) > > > > Btw, you can also read about that at: > > > > https://lwn.net/Articles/753274/ > > > >> Anyway, before the removal of GFP_DMA happens, I'd like to better > >> understand why we're using it at media, and if we can, instead, > >> set the DMA bit mask, just like almost all other media drivers > >> that require to confine DMA into a certain range do. In the case > >> of ARM, this is what we currently have: > >> > >> drivers/media/platform/exynos-gsc/gsc-core.c: > >> vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/exynos4-is/fimc-core.c: > >> vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/exynos4-is/fimc-is.c: > >> vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/exynos4-is/fimc-lite.c: > >> vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/mtk-mdp/mtk_mdp_core.c: > >> vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/omap3isp/isp.c: ret = > >> dma_coerce_mask_and_coherent(isp->dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/s5p-g2d/g2d.c: > >> vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/s5p-jpeg/jpeg-core.c: > >> vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32)); > >> drivers/media/platform/s5p-mfc/s5p_mfc.c: > >> DMA_BIT_MASK(32)); > >> drivers/media/platform/s5p-mfc/s5p_mfc.c: > >> DMA_BIT_MASK(32)); > >> drivers/media/platform/s5p-mfc/s5p_mfc.c: > >> vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32)); > > That's clearer now, thank you for the clarification > I am about to send patches for the sti drivers (set the DMA bit mask) Some drivers call vb2_dma_contig_set_max_seg_size() and some call dma_coerce_mask_and_coherent(). Both are likely needed, the former telling the DMA mapping API about the maximum size of a scatter-gather chunk that the device supports (when using vb2-dma-contig that size should really be the full address space supported by the device as we want DMA-contiguous buffers), and the latter telling the DMA mapping API about the address space that is accessible through DMA (and thus in which address range buffers must be placed). I wonder why the omap3isp driver works without a vb2_dma_contig_set_max_seg_size() call. Sakari, any insight ? > >>>>>> drivers/media/spi/cxd2880-spi.c > >>>>>> > >>>>>> Could you please check if GFP_DMA is really needed there, or if it > >>>>>> is just because of some cut-and-paste from some other place? > >>>>> > >>>>> I started looking at that for the omap3isp driver but Sakari beat me > >>>>> at submitting a patch. GFP_DMA isn't needed for omap3isp. > >>>> > >>>> Thank you both for looking into it. -- Regards, Laurent Pinchart
