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drm/mgag200: Add an option to disable Write-Combine

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Unfortunately, the G200 ioburst workaround doesn't work on some
servers like Dell poweredge XR11, XR5610, or HPE XL260. In this case
completely disabling WC is the only option to achieve low-latency.
So this adds a new Kconfig option to disable WC mapping of the G200.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517151050.624797-3-jfalempe@redhat.com
This commit is contained in:
Jocelyn Falempe
2024-05-17 17:09:58 +02:00
parent e7f67d0388
commit b593ea9406
2 changed files with 16 additions and 0 deletions
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10
drivers/gpu/drm/mgag200/Kconfig
View File

@@ -11,3 +11,13 @@ config DRM_MGAG200
MGA G200 desktop chips and the server variants. It requires 0.3.0
of the modesetting userspace driver, and a version of mga driver
that will fail on KMS enabled devices.
config DRM_MGAG200_DISABLE_WRITECOMBINE
bool "Disable Write Combine mapping of VRAM"
depends on DRM_MGAG200 && PREEMPT_RT
help
The VRAM of the G200 is mapped with Write-Combine to improve
performances. This can interfere with real-time tasks; even if they
are running on other CPU cores than the graphics output.
Enable this option only if you run realtime tasks on a server with a
Matrox G200.

6
drivers/gpu/drm/mgag200/mgag200_drv.c
View File

@@ -146,12 +146,18 @@ int mgag200_device_preinit(struct mga_device *mdev)
}
mdev->vram_res = res;
#if defined(CONFIG_DRM_MGAG200_DISABLE_WRITECOMBINE)
mdev->vram = devm_ioremap(dev->dev, res->start, resource_size(res));
if (!mdev->vram)
return -ENOMEM;
#else
mdev->vram = devm_ioremap_wc(dev->dev, res->start, resource_size(res));
if (!mdev->vram)
return -ENOMEM;
/* Don't fail on errors, but performance might be reduced. */
devm_arch_phys_wc_add(dev->dev, res->start, resource_size(res));
#endif
return 0;
}