From b7792d8b54cc0e66b94d625d70761d086cad1dd3 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Mon, 14 Dec 2015 18:23:43 +0200 Subject: [PATCH] drm/i915: Wait for pipe to start before sampling vblank timestamps on gen2 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit We use the vblank timestamps to generate the vblank frame counter value on gen2. That means we need the pipe scanout position to be accurate when we call drm_crtc_vblank_on(), otherwise the frame counter guesstimate may jump when the pipe actually start. What I observed on my 85x is that the DSL initially reads 0, and when the pipe actually starts DSL jumps to vblank_start. On gen2 DSL==0 means actually vtotal-1 (see update_scanline_offset()), so if we initially get vtotal-1, and then very quickly vblank_start (or thereabouts), the scanout position will appear to jump backwards by approximately one vblank length. Which means the frame counter guesstimate will also jump backwards. That's no good, so let's make sure the pipe has started before we call drm_crtc_vblank_on(). Signed-off-by: Ville Syrjälä Link: http://patchwork.freedesktop.org/patch/msgid/1450110229-30450-5-git-send-email-ville.syrjala@linux.intel.com Reviewed-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_display.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 20e99a0c5536..9c87d5784f1a 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -2151,6 +2151,17 @@ static void intel_enable_pipe(struct intel_crtc *crtc) I915_WRITE(reg, val | PIPECONF_ENABLE); POSTING_READ(reg); + + /* + * Until the pipe starts DSL will read as 0, which would cause + * an apparent vblank timestamp jump, which messes up also the + * frame count when it's derived from the timestamps. So let's + * wait for the pipe to start properly before we call + * drm_crtc_vblank_on() + */ + if (dev->max_vblank_count == 0 && + wait_for(intel_get_crtc_scanline(crtc) != crtc->scanline_offset, 50)) + DRM_ERROR("pipe %c didn't start\n", pipe_name(pipe)); } /** -- 2.20.1