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SubjectRe: [PATCH] drm: Permit video-buffers writecombine mapping for MIPS
Hi Serge,

On Tue, Apr 23, 2019 at 03:31:22PM +0300, Serge Semin wrote:
> Since commit 4b050ba7a66c ("MIPS: pgtable.h: Implement the
> pgprot_writecombine function for MIPS") and commit c4687b15a848 ("MIPS: Fix
> definition of pgprot_writecombine()") write-combine vma mapping is
> available to be used by kernel subsystems for MIPS. In particular the
> uncached accelerated attribute is requested to be set by ioremap_wc()
> method and by generic PCI memory pages/ranges mapping methods. The same
> is done by the drm_io_prot()/ttm_io_prot() functions in case if
> write-combine flag is set for vma's passed for mapping. But for some
> reason the pgprot_writecombine() method calling is ifdefed to be a
> platform-specific with MIPS system being marked as lacking of one. At the
> very least it doesn't reflect the current MIPS platform implementation.
> So in order to improve the DRM subsystem performance on MIPS with UCA
> mapping enabled, we need to have pgprot_writecombine() called for buffers,
> which need store operations being combined. In case if particular MIPS
> chip doesn't support the UCA attribute, the mapping will fall back to
> noncached.
> Cc: Ralf Baechle <>
> Cc: Paul Burton <>
> Cc: James Hogan <>
> Signed-off-by: Vadim V. Vlasov <>
> Signed-off-by: Serge Semin <>
> ---
> drivers/gpu/drm/drm_vm.c | 5 +++--
> drivers/gpu/drm/ttm/ttm_bo_util.c | 4 ++--
> 2 files changed, 5 insertions(+), 4 deletions(-)

Looks good to me:

Reviewed-by: Paul Burton <>


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