Ville Syrjälä c2b6337446 drm/i915: Enable DPLL VGA mode before P1/P2 divider write ... Apparently writing the DPLL register P1/P2 divider fields won't trigger an actual change in the DPLL output unless VGA mode is enabled for prior to the register write that changes the P1/P2 dividers. The write with the new P1/P2 divider can itself disable VGA mode again without problems. I tested the behaviour on my 946GZ, and when manually frobbing the register with the display on, the behaviour is very clear. However I can't explain why this machine actually works. The P1/P2 divider changes caused by normal modesets do seem to make it through to the hardware somehow since I get a stable picture on the monitor with any resolution. Maybe it's the "three times for luck" stuff that somehow masks the problem, or something. But apparently there are machines (eg. Nick Bowler's G45) where that isn't the case and we fail to get the correct clock from the DPLL. Things used to work because we enabled VGA mode for disabled DPLLs, so when re-enabling the DPLL VGA mode was enabled just prior to the first register write, and hence the P1/P2 change went through without a hitch. That got changed in b8afb9113c drm/i915: Keep GMCH DPLL VGA mode always disabled in the name of consistency. In order to keep the consistency part, leave VGA mode disabled for disabled DPLLs, but turn it on just prior to updating the P1/P2 dividers to make sure the hardware picks up on the new values. Cc: Nick Bowler <nbowler@draconx.ca> Reported-by: Nick Bowler <nbowler@draconx.ca> Tested-by: Nick Bowler <nbowler@draconx.ca> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Jani Nikula <jani.nikula@intel.com>		2015-10-13 17:03:38 +03:00
..
drm	drm/i915: Enable DPLL VGA mode before P1/P2 divider write	2015-10-13 17:03:38 +03:00
host1x	gpu: host1x: mipi: Power down regulators when unused	2015-08-13 13:47:21 +02:00
ipu-v3	gpu/drm: Kill off set_irq_flags usage	2015-09-16 16:53:38 +02:00
vga	vga_switcheroo: Remove unnecessary checks	2015-08-12 17:13:19 +02:00
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