This is a note to let you know that I've just added the patch titled ARM: dma-api: fix max_pfn off-by-one error in __dma_supported() to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm-dma-api-fix-max_pfn-off-by-one-error-in-__dma_supported.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From f3cc4e1d44a813a0685f2e558b78ace3db559722 Mon Sep 17 00:00:00 2001 From: Chen-Yu Tsai <wens@xxxxxxxx> Date: Mon, 3 Feb 2020 17:37:48 -0800 Subject: ARM: dma-api: fix max_pfn off-by-one error in __dma_supported() From: Chen-Yu Tsai <wens@xxxxxxxx> commit f3cc4e1d44a813a0685f2e558b78ace3db559722 upstream. max_pfn, as set in arch/arm/mm/init.c: static void __init find_limits(unsigned long *min, unsigned long *max_low, unsigned long *max_high) { *max_low = PFN_DOWN(memblock_get_current_limit()); *min = PFN_UP(memblock_start_of_DRAM()); *max_high = PFN_DOWN(memblock_end_of_DRAM()); } with memblock_end_of_DRAM() pointing to the next byte after DRAM. As such, max_pfn points to the PFN after the end of DRAM. Thus when using max_pfn to check DMA masks, we should subtract one when checking DMA ranges against it. Commit 8bf1268f48ad ("ARM: dma-api: fix off-by-one error in __dma_supported()") fixed the same issue, but missed this spot. This issue was found while working on the sun4i-csi v4l2 driver on the Allwinner R40 SoC. On Allwinner SoCs, DRAM is offset at 0x40000000, and we are starting to use of_dma_configure() with the "dma-ranges" property in the device tree to have the DMA API handle the offset. In this particular instance, dma-ranges was set to the same range as the actual available (2 GiB) DRAM. The following error appeared when the driver attempted to allocate a buffer: sun4i-csi 1c09000.csi: Coherent DMA mask 0x7fffffff (pfn 0x40000-0xc0000) covers a smaller range of system memory than the DMA zone pfn 0x0-0xc0001 sun4i-csi 1c09000.csi: dma_alloc_coherent of size 307200 failed Fixing the off-by-one error makes things work. Link: http://lkml.kernel.org/r/20191224030239.5656-1-wens@xxxxxxxxxx Fixes: 11a5aa32562e ("ARM: dma-mapping: check DMA mask against available memory") Fixes: 9f28cde0bc64 ("ARM: another fix for the DMA mapping checks") Fixes: ab746573c405 ("ARM: dma-mapping: allow larger DMA mask than supported") Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Robin Murphy <robin.murphy@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm/mm/dma-mapping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -221,7 +221,7 @@ EXPORT_SYMBOL(arm_coherent_dma_ops); static int __dma_supported(struct device *dev, u64 mask, bool warn) { - unsigned long max_dma_pfn = min(max_pfn, arm_dma_pfn_limit); + unsigned long max_dma_pfn = min(max_pfn - 1, arm_dma_pfn_limit); /* * Translate the device's DMA mask to a PFN limit. This Patches currently in stable-queue which might be from wens@xxxxxxxx are queue-5.4/mfd-axp20x-mark-axp20x_vbus_ipsout_mgmt-as-volatile.patch queue-5.4/power-supply-axp20x_ac_power-fix-reporting-online-status.patch queue-5.4/arm-dma-api-fix-max_pfn-off-by-one-error-in-__dma_supported.patch