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由 Ville Syrjälä 提交于
Sometimes (exactly when is a bit unclear) DISPLAY_PHY_CONTROL appears to get corrupted. The values I've managed to read from it seem to have some pattern but vary quite a lot. The corruption doesn't seem to just happen when the register is accessed, but can also happen spontaneosly during modeset. When this happens during a modeset things go south and the display doesn't light up. I've managed to hit the problemn when toggling HDMI on port D on and off. When things get corrupted the display doesn't light up, but as soon as I manually write the correct value to the register the display comes up. First I was suspicious that we ourselves accidentally overwrite it with garbage, but didn't catch anything with the reg_rw tracepoint. Also I sprinkled check all over the modeset path to see exactly when the corruption happens, and eg. the read back value was fine just before intel_dp_set_m(), and corrupted immediately after it. I also made my check function repair the register value whenever it was wrong, and with this approach the corruption repeated several times during the modeset operation, always seeming to trigger in the same exact calls to the check function, while other calls to the function never caught anything. So far I've not seen this problem occurring when carefully avoiding all read accesses to DISPLAY_PHY_CONTROL. Not sure if that's just pure luck or an actual workaround, but we can hope it works. So let's avoid reading the register and instead track the desired value of the register in dev_priv. v2: Read out the power well state to determine initial register value v3: Use DPIO_CHx names instead of raw numbers Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: NDeepak S <deepak.s@linux.intel.com> Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
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