On Tue, Oct 06, 2015 at 11:42:33AM -0400, Nick Bowler wrote:
Hi,
This issue is still present in 4.3-rc4.
On 9/24/15, Nick Bowler nbowler@draconx.ca wrote:
Testing out 4.3-rc2, first thing I notice is that the VGA output is not working. Specifically, the display is continuously powering on and off -- at no point is any image visible on the screen (I am expecting to see the console output). The display connected to the HDMI output is working fine.
Linux 4.2 did not suffer from this problem.
In dmesg I see the following messages, which I do not see on a working kernel. Full dmesg from 4.3-rc2 is attached (gzipped).
[ 0.115339] [drm:drm_calc_timestamping_constants] *ERROR* crtc 21: Can't calculate constants, dotclock = 0! [ 0.117582] [drm:intel_opregion_init] *ERROR* No ACPI video bus found
This is an older machine with Intel G45 graphics.
I was able to identify the commit which fixed my boot crashes, so I cherry-picked 80aa93128653 ("drm/i915: disable_shared_pll doesn't work on pre-gen5") on top of all otherwise untestable commits. This allowed bisection to proceed:
b8afb9113c519a8bd742f7df8c424b0af69a75cd is the first bad commit commit b8afb9113c519a8bd742f7df8c424b0af69a75cd Author: Ville Syrjälä ville.syrjala@linux.intel.com Date: Mon Jun 29 15:25:48 2015 +0300
drm/i915: Keep GMCH DPLL VGA mode always disabled We disable the DPLL VGA mode when enabling the DPLL, but we enaable it again when disabling the DPLL. Having VGA mode enabled even in unused DPLLs can cause problems for CHV, so it seems wiser to always keep it disabled. And let's just do that on all GMCH platforms to keep things as similar as possible between them. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>:040000 040000 7797d596e73ecf75723375028decd25fbe332ee0 9f90a92eec483919853d68563bbb09a71a305532 M drivers
Unfortunately it does not revert cleanly on master.
@@ -1790,13 +1790,13 @@ static void i9xx_disable_pll(struct intel_crtc *crtc) /* Make sure the pipe isn't still relying on us */ assert_pipe_disabled(dev_priv, pipe);
- I915_WRITE(DPLL(pipe), 0); + I915_WRITE(DPLL(pipe), DPLL_VGA_MODE_DIS); POSTING_READ(DPLL(pipe)); }
That hunk is the only relevant part for your machine. Can you try to revert just that manually?
But I'm really surprised that would have any effect since we only used to enable "VGA mode" when the DPLL is off. And when the DPLL is off, there's nothing on the screen anyway.