drm/i915/vlv: Add cdclk workaround for DSI
At least on the Chuwi Vi8 (non pro/plus) the LCD panel will show an image shifted aprox. 20% to the left (with wraparound) and sometimes also wrong colors, showing that the panel controller is starting with sampling the datastream somewhere mid-line. This happens after the first blanking and re-init of the panel. After looking at drm.debug output I noticed that initially we inherit the cdclk of 333333 KHz set by the GOP, but after the re-init we picked 266667 KHz, which turns out to be the cause of this problem, a quick hack to hard code the cdclk to 333333 KHz makes the problem go away. I've tested this on various Bay Trail devices, to make sure this not does cause regressions on other devices and the higher cdclk does not cause any problems on the following devices: -GP-electronic T701 1024x600 333333 KHz cdclk after this patch -PEAQ C1010 1920x1200 333333 KHz cdclk after this patch -PoV mobii-wintab-800w 800x1280 333333 KHz cdclk after this patch -Asus Transformer-T100TA 1368x768 320000 KHz cdclk after this patch Also interesting wrt this is the comment in vlv_calc_cdclk about the existing workaround to avoid 200 Mhz as clock because that causes issues in some cases. This commit extends the "do not use 200 Mhz" workaround with an extra check to require atleast 320000 KHz (avoiding 266667 KHz) when a DSI panel is active. Changes in v2: -Change the commit message and the code comment to not treat the GOP as a reference, the GOP should not be treated as a reference Acked-by:Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by:
Hans de Goede <hdegoede@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171220105017.11259-1-hdegoede@redhat.com (cherry picked from commit c8dae55a ) Signed-off-by:
Rodrigo Vivi <rodrigo.vivi@intel.com>
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