Commit b593ea94 authored by Jocelyn Falempe's avatar Jocelyn Falempe
Browse files

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



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: default avatarJocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517151050.624797-3-jfalempe@redhat.com
parent e7f67d03

drivers/gpu/drm/mgag200/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -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.
 
 No newline at end of file

drivers/gpu/drm/mgag200/mgag200_drv.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

}