On Mon, 09 Feb 2015, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > On Mon, Feb 09, 2015 at 03:15:56PM +0200, Jani Nikula wrote: >> On Wed, 26 Nov 2014, Paulo Zanoni <przanoni@xxxxxxxxx> wrote: >> > 2014-11-24 13:54 GMT-02:00 Daniel Vetter <daniel.vetter@xxxxxxxx>: >> >> Nothing in Bspec seems to indicate that we actually needs this, and it >> >> looks like can't work since by this point the pipe is off and so >> >> vblanks won't really happen any more. >> >> >> >> Note that Bspec mentions that it takes a vblank for this bit to >> >> change, but _only_ when enabling. >> >> >> >> Dropping this code quenches an annoying backtrace introduced by the >> >> more anal checking since >> >> >> >> commit 51e31d49c89055299e34b8f44d13f70e19aaaad1 >> >> Author: Daniel Vetter <daniel.vetter@xxxxxxxx> >> >> Date: Mon Sep 15 12:36:02 2014 +0200 >> >> >> >> drm/i915: Use generic vblank wait >> >> >> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86095 >> >> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> >> >> --- >> >> drivers/gpu/drm/i915/intel_dp.c | 17 +---------------- >> >> 1 file changed, 1 insertion(+), 16 deletions(-) >> >> >> >> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c >> >> index 46731da407c0..63fcdbf90652 100644 >> >> --- a/drivers/gpu/drm/i915/intel_dp.c >> >> +++ b/drivers/gpu/drm/i915/intel_dp.c >> >> @@ -3514,8 +3514,6 @@ intel_dp_link_down(struct intel_dp *intel_dp) >> >> enum port port = intel_dig_port->port; >> >> struct drm_device *dev = intel_dig_port->base.base.dev; >> >> struct drm_i915_private *dev_priv = dev->dev_private; >> >> - struct intel_crtc *intel_crtc = >> >> - to_intel_crtc(intel_dig_port->base.base.crtc); >> >> uint32_t DP = intel_dp->DP; >> >> >> >> if (WARN_ON(HAS_DDI(dev))) >> >> @@ -3540,8 +3538,6 @@ intel_dp_link_down(struct intel_dp *intel_dp) >> >> >> >> if (HAS_PCH_IBX(dev) && >> >> I915_READ(intel_dp->output_reg) & DP_PIPEB_SELECT) { >> >> - struct drm_crtc *crtc = intel_dig_port->base.base.crtc; >> >> - >> >> /* Hardware workaround: leaving our transcoder select >> >> * set to transcoder B while it's off will prevent the >> >> * corresponding HDMI output on transcoder A. >> >> @@ -3552,18 +3548,7 @@ intel_dp_link_down(struct intel_dp *intel_dp) >> >> */ >> >> DP &= ~DP_PIPEB_SELECT; >> >> I915_WRITE(intel_dp->output_reg, DP); >> >> - >> >> - /* Changes to enable or select take place the vblank >> >> - * after being written. >> >> - */ >> >> - if (WARN_ON(crtc == NULL)) { >> >> - /* We should never try to disable a port without a crtc >> >> - * attached. For paranoia keep the code around for a >> >> - * bit. */ >> >> - POSTING_READ(intel_dp->output_reg); >> >> - msleep(50); >> >> - } else >> >> - intel_wait_for_vblank(dev, intel_crtc->pipe); >> > >> > What I can guess is that we have the vblank wait here because the >> > DP_PORT_EN bit is still enabled at this point. It would make some >> > sense to have it if the pipe were not off... So removing the waits >> > looks sane: Reviewed-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx> >> > >> > But when I read the spec, it makes me think that maybe doing the >> > I915_WRITE above is also wrong, since the port is still enabled. Maybe >> > we should only clear bit 30 in the same write as the one that clears >> > bit 31? >> >> Ugh. So the spec says, "When disabling the port, software must >> temporarily enable the port with transcoder select (bit #30) cleared to >> ‘0’ after disabling the port." >> >> IIUC we should disable like we normally do, and do the w/a by enabling >> and disabling the port with DP_PIPEB_SELECT cleared *after* that. I >> think the current code is wrong, the patch is wrong, what Paulo suggests >> is wrong, and also intel_disable_hdmi() is wrong. > > This code has been bugging me for a long time as well. IIRC I even had > cooked up some patches to do the re-enable as you suggest since I > read the spec the same way. But I never had enough time to test it. And > in order to really test it I would first like to actually reproduce the > problem that the workaround is supposed to fix. How else would you know > if the workaround is correct after all. *sigh* an alternative is to apply Daniel's patch and add a comment there's something fishy. Jani. > > -- > Ville Syrjälä > Intel OTC -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
