[PATCH] drm/radeon: TTM must be init with cpu-visible VRAM (original) (raw)

Christian König deathsimple at vodafone.de
Fri Feb 28 09:27:26 PST 2014

Am 28.02.2014 17:52, schrieb Lauri Kasanen:

On Fri, 28 Feb 2014 16:43:54 +0100 Christian König <deathsimple at vodafone.de> wrote:

Am 27.02.2014 22:38, schrieb Lauri Kasanen: Without this, a bo may get created in the cpu-inaccessible vram. Before the CP engines get setup, all copies are done via cpu memcpy.

This means that the cpu tries to read from inaccessible memory, fails, and the radeon module proceeds to disable acceleration. Doing this has no downsides, as the real VRAM size gets set as soon as the CP engines get init. This is a candidate for 3.14 fixes. This should be unnecessary, since TTM gets initialized only seeing the visible VRAM and later on radeonttmsetactivevramsize gets called to increase the limit. If this isn't the case any more we should figure out why instead of working around it like this. Negative, TTM gets initialized with realvram just a few lines above this patch, not visiblevram. git blame shows 7a50f01a from 2009, "drm/radeon/kms: vram sizing on certain r100 chips needs workaround." by Dave Airlie. So the TTM VRAM init has been wrong for five years, and only worked by accident because until now all allocations were done bottom-up. Yeah, just came to the same conclusion. We probably never hit the case in the last five years because we don't really access the memory before we start the copy ring. Please fix ttmboinitmm to use rdev->mc.visiblevramsize instead. That allocations are made bottom-up is relied upon in a couple of other cases as well, the stolen VGA memory and the UVD firmware handling for example. I initially did that, but it caused some issues. I didn't investigage it further, but I guess it has to be init to the maximum size, and then only the size lowered, so that the change only affects lpfn.

Fair enough, probably something gets allocated on init or something like that.

Please document that with a comment and resend the patch.

Christian.

- Lauri

More information about the dri-devel mailing list