648a9bc530
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@karolherbst.de> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91317 Testcase: igt/gem_reg_read Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Michał Winiarski <michal.winiarski@intel.com> Cc: stable@vger.kernel.org Tested-by: Michał Winiarski <michal.winiarski@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> |
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