linux-kernel - Re: [RFC PATCH 0/2] drm/ttm: support device w/o coherency

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Message-ID: <2a087cc4-1c17-4c00-839a-6736bdba2b73@amd.com>
Date: Mon, 1 Jul 2024 13:37:37 +0200
From: Christian König <christian.koenig@....com>
To: Icenowy Zheng <uwu@...nowy.me>, Huang Rui <ray.huang@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] drm/ttm: support device w/o coherency

Am 29.06.24 um 07:22 schrieb Icenowy Zheng:
> This patchset tries to make TTM support devices w/o full DMA coherency
> capability (usually due to part of the link between the device and the
> CPU, esp. PCIe controller, do not have full coherency).
>
> The patchset itself looks quite straightforward, however I don't know
> why this isn't included in the kernel in years, so make it a RFC.

Well that's already supported your driver just need to request uncached 
TT allocations.

Regards,
Christian.

>
> Tested on Rockchip RK3566, which has a PCIe controller w/o full
> coherency with an AMD OLAND GPU (R7 240). Mainly radeon driver is
> tested, but amdgpu driver is tried and at least OpenGL (glmark2) works.
> (The board used for testing is a Quartz64, which has a PCIe slot that
> can directly be seated with a PCIe graphics card)
>
> Icenowy Zheng (2):
>    drm/ttm: save the device's DMA coherency status in ttm_device
>    drm/ttm: downgrade cached to write_combined when snooping not
>      available
>
>   drivers/gpu/drm/ttm/ttm_bo_util.c | 4 ++++
>   drivers/gpu/drm/ttm/ttm_device.c  | 2 ++
>   drivers/gpu/drm/ttm/ttm_tt.c      | 4 ++++
>   include/drm/ttm/ttm_caching.h     | 3 ++-
>   include/drm/ttm/ttm_device.h      | 5 +++++
>   5 files changed, 17 insertions(+), 1 deletion(-)
>