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SubjectRe: [PATCH] powerpc: ensure that swiotlb buffer is allocated from low memory
Date
Mike Rapoport <rppt@kernel.org> writes:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> Some powerpc platforms (e.g. 85xx) limit DMA-able memory way below 4G. If a
> system has more physical memory than this limit, the swiotlb buffer is not
> addressable because it is allocated from memblock using top-down mode.
>
> Force memblock to bottom-up mode before calling swiotlb_init() to ensure
> that the swiotlb buffer is DMA-able.
>
> Link: https://lkml.kernel.org/r/F1EBB706-73DF-430E-9020-C214EC8ED5DA@xenosoft.de

This wasn't bisected, but I thought it was a regression. Do we know what
commit caused it?

Was it 25078dc1f74b ("powerpc: use mm zones more sensibly") ?

Or was that a red herring?

cheers

> Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Darren Stevens <darren@stevens-zone.net>
> Cc: mad skateman <madskateman@gmail.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Rob Herring <robh+dt@kernel.org>
> ---
> arch/powerpc/mm/mem.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index be941d382c8d..14c2c53e3f9e 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -260,6 +260,14 @@ void __init mem_init(void)
> BUILD_BUG_ON(MMU_PAGE_COUNT > 16);
>
> #ifdef CONFIG_SWIOTLB
> + /*
> + * Some platforms (e.g. 85xx) limit DMA-able memory way below
> + * 4G. We force memblock to bottom-up mode to ensure that the
> + * memory allocated in swiotlb_init() is DMA-able.
> + * As it's the last memblock allocation, no need to reset it
> + * back to to-down.
> + */
> + memblock_set_bottom_up(true);
> swiotlb_init(0);
> #endif
>
> --
> 2.24.0

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