linux-kernel - Re: [PATCH] drm: Permit video-buffers writecombine mapping for MIPS

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Date:   Tue, 23 Apr 2019 17:52:06 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     Serge Semin <fancer.lancer@...il.com>
CC:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Junwei Zhang <Jerry.Zhang@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "Vadim V . Vlasov" <vadim.vlasov@...latforms.ru>
Subject: Re: [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 <ralf@...ux-mips.org>
> Cc: Paul Burton <paul.burton@...s.com>
> Cc: James Hogan <jhogan@...nel.org>
> Signed-off-by: Vadim V. Vlasov <vadim.vlasov@...latforms.ru>
> Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> ---
>  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 <paul.burton@...s.com>

Thanks,
    Paul