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.
The phenomen was first observed on a 32bit system which offset the value by 32bits, but recently even 64bit Haswell systems have been demonstrated to return complete garbage instead. Reported-by: Karol Herbst <freedesk...@karolherbst.de> Tested-by: Karol Herbst <freedesk...@karolherbst.de> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91317 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: sta...@vger.kernel.org --- drivers/gpu/drm/i915/intel_uncore.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c index 2c477663d378..66fdc85697f6 100644 --- a/drivers/gpu/drm/i915/intel_uncore.c +++ b/drivers/gpu/drm/i915/intel_uncore.c @@ -1325,7 +1325,7 @@ int i915_reg_read_ioctl(struct drm_device *dev, switch (entry->size) { case 8: - reg->val = I915_READ64(reg->offset); + reg->val = I915_READ64_2x32(reg->offset, reg->offset+4); break; case 4: reg->val = I915_READ(reg->offset); -- 2.1.4 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
