From: Mario Kleiner Date: Wed, 30 Oct 2013 04:13:08 +0000 (+0100) Subject: drm/intel: Push get_scanout_position() timestamping into kms driver. X-Git-Tag: v3.13-rc1~76^2~60 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad3543ede630fa38b3b606f24b9b9c3e16d8af13;p=pandora-kernel.git drm/intel: Push get_scanout_position() timestamping into kms driver. Move the ktime_get() clock readouts and potential preempt_disable() calls from drm core into kms driver to make it compatible with the api changes in the drm core. The intel-kms driver needs to take the uncore.lock inside i915_get_crtc_scanoutpos() and intel_pipe_in_vblank(). This is incompatible with the preempt_disable() on a PREEMPT_RT patched kernel, as regular spin locks must not be taken within a preempt_disable'd section. Lock contention on the uncore.lock also introduced too much uncertainty in vblank timestamps. Push the ktime_get() timestamping for scanoutpos queries and potential preempt_disable_rt() into i915_get_crtc_scanoutpos(), so these problems can be avoided: 1. First lock the uncore.lock (might sleep on a PREEMPT_RT kernel). 2. preempt_disable_rt() (will be added by the rt-linux folks). 3. ktime_get() a timestamp before scanout pos query. 4. Do all mmio reads as fast as possible without grabbing any new locks! 5. ktime_get() a post-query timestamp. 6. preempt_enable_rt() 7. Unlock the uncore.lock. This reduces timestamp uncertainty on a low-end HP Atom Mini netbook with Intel GMA-950 nicely: Before: 3-8 usecs with spikes > 20 usecs, triggering query retries. After : Typically 1 usec (98% of all samples), occassionally 2 usecs (2% of all samples), with maximum of 3 usecs (a handful). v2: Fix formatting of new multi-line code comments. Signed-off-by: Mario Kleiner Reviewed-by: Ville Syrjälä Reviewed-by: Alex Deucher Signed-off-by: Dave Airlie --- Reading git-diff-tree failed