[Intel-gfx] [PATCH v3] drm/i915: Use two 32bit reads for select 64bit REG_READ ioctls

[Chris Wilson]

On Tue, Jul 21, 2015 at 08:49:31AM +0200, Daniel Vetter wrote:
> On Fri, Jul 17, 2015 at 05:10:25PM +0200, Michał Winiarski wrote:
> > On Thu, Jul 16, 2015 at 12:37:56PM +0100, Chris Wilson wrote:
> > > Since the hardware sometimes mysteriously totally flummoxes the 64bit
> > > read of a 64bit register when read using a single instruction, split the
> > > read into two instructions. Since the read here is of automatically
> > > incrementing timestamp counters, we also have to be very careful in
> > > order to make sure that it does not increment between the two
> > > instructions.
> > > 
> > > However, since userspace tried to workaround this issue and so enshrined
> > > this ABI for a broken hardware read and in the process neglected that
> > > the read only fails in some environments, we have to introduce a new
> > > uABI flag for userspace to request the 2x32 bit accurate read of the
> > > timestamp.
> > > 
> > > v2: Fix alignment check and include details of the workaround for
> > > userspace.
> > > 
> > > Reported-by: Karol Herbst <freedesktop at karolherbst.de>
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91317
> > > Testcase: igt/gem_reg_read
> > Tested-by: Michał Winiarski <michal.winiarski at intel.com>
> 
> Where are the mesa/beignet/libva patches for this?

Trivial. Absolutely trivial. Just waiting for the kernel.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre