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Chen-Yu Tsai
f3cc4e1d44
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 8bf1268f48 ("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@kernel.org
Fixes: 11a5aa3256 ("ARM: dma-mapping: check DMA mask against available memory")
Fixes: 9f28cde0bc ("ARM: another fix for the DMA mapping checks")
Fixes: ab746573c4 ("ARM: dma-mapping: allow larger DMA mask than supported")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.