From 5ade2c2f5813733f23bbb2f21e8ba5c3f8474a2b Mon Sep 17 00:00:00 2001 From: Paulo Zanoni Date: Thu, 19 Sep 2013 17:03:06 -0300 Subject: [PATCH] drm/i915: wait for IPS_ENABLE when enabling IPS At the end of haswell_crtc_enable we have an intel_wait_for_vblank with a big comment, and the message suggests it's a workaround for something we don't really understand. So I removed that wait and started getting HW state readout error messages saying that the IPS state is not what we expected. I investigated and concluded that after you write IPS_ENABLE to IPS_CTL, the bit will only actually become 1 on the next vblank. So add code to wait for the IPS_ENABLE bit. We don't really need this wait right now due to the wait I already mentioned, but at least this one has a reason to be there, while the other one is just to workaround some problem: we may remove it in the future. The wait also acts as a POSTING_READ which we missed. Signed-off-by: Paulo Zanoni Reviewed-by: Chris Wilson Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_display.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index a6d8698d36a1..f5126b81b435 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -3346,6 +3346,14 @@ void hsw_enable_ips(struct intel_crtc *crtc) * for a vblank, so all we need to do here is to enable the IPS bit. */ assert_plane_enabled(dev_priv, crtc->plane); I915_WRITE(IPS_CTL, IPS_ENABLE); + + /* The bit only becomes 1 in the next vblank, so this wait here is + * essentially intel_wait_for_vblank. If we don't have this and don't + * wait for vblanks until the end of crtc_enable, then the HW state + * readout code will complain that the expected IPS_CTL value is not the + * one we read. */ + if (wait_for(I915_READ_NOTRACE(IPS_CTL) & IPS_ENABLE, 50)) + DRM_ERROR("Timed out waiting for IPS enable\n"); } void hsw_disable_ips(struct intel_crtc *crtc) -- 2.20.1