At Mon, 27 Feb 2012 12:17:57 +0000, Chris Wilson wrote: > > On Mon, 27 Feb 2012 12:39:24 +0100, Takashi Iwai <tiwai at suse.de> wrote: > > It seems that writing DSPSURF in intel_flush_display_plane() causes > > the blank screen on some old laptops like Dell D630 with 965GM. > > Since this operation is needed only for ILK+, make it conditional. > > The specs say that DSPASURF is the latch register for updates of the DSPA > registers on gen4 (including 965gm) as well. Presumably the bug is that > we only partially update the DSPA registers prior to the first call to > intel_flush_display_plane() which this papers over by disabling the > update until a valid address is written to DSPASURF. And there is such a > spurious call to intel_enable_plane() prior to us setting a valid > scanout surface: Sounds reasonable. FWIW, the change was first introduced in commit [b24e7179: drm/i915: add pipe/plane enable/disable functions], then in commit [efc2924e: drm/i915: Call intel_enable_plane from i9xx_crtc_mode_set (again)], it's placed into i9xx_crtc_mode_set(). This explains the fact that it was discovered only on old machines as i9xx_crtc_mode_set() is the only crtc_mode_set op calling intel_enable_plane(). BTW, the bisection leaded to a merge commit, so the bug is really depending on the activation path or timing. I'll ask a tester to try your patch. thanks, Takashi > diff --git a/drivers/gpu/drm/i915/intel_display.c > b/drivers/gpu/drm/i915/intel_d > index 66b19d3..ea8e4a1 100644 > --- a/drivers/gpu/drm/i915/intel_display.c > +++ b/drivers/gpu/drm/i915/intel_display.c > @@ -5453,7 +5453,6 @@ static int i9xx_crtc_mode_set(struct drm_crtc > *crtc, > > I915_WRITE(DSPCNTR(plane), dspcntr); > POSTING_READ(DSPCNTR(plane)); > - intel_enable_plane(dev_priv, plane, pipe); > > ret = intel_pipe_set_base(crtc, x, y, old_fb); > > -Chris > > -- > Chris Wilson, Intel Open Source Technology Centre >
