On Wednesday, February 15, 2017 12:12:50 AM PST Chris Wilson wrote: > On Tue, Feb 14, 2017 at 08:17:51PM -0800, Kenneth Graunke wrote: > > This patch makes the I915_PARAM_HAS_EXEC_CONSTANTS getparam return 0 > > (indicating the optional feature is not supported), and makes execbuf > > always return -EINVAL if the flags are used. > > > > Apparently, no userspace ever shipped which used this optional feature: > > I checked the git history of Mesa, xf86-video-intel, libva, and Beignet, > > and there were zero commits showing a use of these flags. Kernel commit > > 72bfa19c8deb4 apparently introduced the feature prematurely. > > It was actually cairo where we had patches to use it first. And we then > realised the use was broken for gen6. Ahhh, that makes sense. I knew I was forgetting about some userspace. Thanks for reminding me about cairo-drm. > > 'relative_constants_mode' has always been tracked per-device, but this > > has actually been wrong ever since hardware contexts were introduced, as > > the INSTPM register is saved (and automatically restored) as part of the > > render ring context. The software per-device value could therefore get > > out of sync with the hardware per-context value. This meant that using > > them is actually unsafe: a client which tried to use them could damage > > the state of other clients, causing the GPU to interpret their BO > > offsets as absolute pointers, leading to bogus memory reads. > > > > These flags were also never ported to execlist mode, making them no-ops > > on Gen9+ (which requires execlists), and Gen8 in the default mode. > > > > On Gen8+, userspace can write these registers directly, achieving the > > same effect. On Gen6-7.5, it likely makes sense to extend the command > > parser to support them. I don't think anyone wants this on Gen4-5. > > > > Based on a patch by Dave Gordon. > > > > Cc: Dave Gordon <david.s.gordon@xxxxxxxxx> > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92448 > > Signed-off-by: Kenneth Graunke <kenneth@xxxxxxxxxxxxx> > > --- > > drivers/gpu/drm/i915/i915_drv.c | 2 +- > > drivers/gpu/drm/i915/i915_drv.h | 2 -- > > drivers/gpu/drm/i915/i915_gem.c | 2 -- > > drivers/gpu/drm/i915/i915_gem_execbuffer.c | 50 ++---------------------------- > > 4 files changed, 3 insertions(+), 53 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c > > index 309c29c84c54..1a53a4bb09c8 100644 > > --- a/drivers/gpu/drm/i915/i915_drv.c > > +++ b/drivers/gpu/drm/i915/i915_drv.c > > @@ -276,7 +276,7 @@ static int i915_getparam(struct drm_device *dev, void *data, > > value = !!dev_priv->engine[VCS2]; > > break; > > case I915_PARAM_HAS_EXEC_CONSTANTS: > > - value = INTEL_GEN(dev_priv) >= 4; > > + value = 0; > > The style for obsolete param is to return -ENODEV. If that makes sense > we can move this to the start of this block with the other dead params. > > Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > -Chris Thanks, I missed that! I'll change this and send a v3.
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