[PATCH] backport commit bb98e72adaf9d19719aba35f802d4836f5d5176c to 4.4.49 fixed i915 dsi init bug passed test on my Lenovo Miix 2 8 (Bay Trail Z3740)

From: River Zhou
Date: Thu Feb 16 2017 - 23:50:19 EST

commit bb98e72adaf9d19719aba35f802d4836f5d5176c
Author: Hans de Goede <hdegoede@xxxxxxxxxx>
Date: Fri Dec 2 15:29:04 2016 +0100

drm/i915/dsi: Do not clear DPOUNIT_CLOCK_GATE_DISABLE from vlv_init_display_clock_gating

On my Cherrytrail CUBE iwork8 Air tablet PIPE-A would get stuck on loading
i915 at boot 1 out of every 3 boots, resulting in a non functional LCD.
Once the i915 driver has successfully loaded, the panel can be disabled /
enabled without hitting this issue.

The getting stuck is caused by vlv_init_display_clock_gating() clearing
the DPOUNIT_CLOCK_GATE_DISABLE bit in DSPCLK_GATE_D when called from
chv_pipe_power_well_ops.enable() on driver load, while a pipe is enabled
driving the DSI LCD by the BIOS.

Clearing this bit while DSI is in use is a known issue and
intel_dsi_pre_enable() / intel_dsi_post_disable() already set / clear it
as appropriate.

This commit modifies vlv_init_display_clock_gating() to leave the
DPOUNIT_CLOCK_GATE_DISABLE bit alone fixing the pipe getting stuck.

Changes in v2:
-Replace PIPE-A with "a pipe" or "the pipe" in the commit msg and

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97330
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Reviewed-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/20161202142904.25613-1-hdegoede@xxxxxxxxxx
Signed-off-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
(cherry picked from commit 721d484563e1a51ada760089c490cbc47e909756)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>

Signed-off-by: River Zhou <riverzhou2000@xxxxxxx>
drivers/gpu/drm/i915/intel_pm.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 3f80216..e7c1851 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6803,7 +6803,18 @@ static void ivybridge_init_clock_gating(struct drm_device *dev)

static void vlv_init_display_clock_gating(struct drm_i915_private *dev_priv)
+ u32 val;
+ /*
+ * On driver load, a pipe may be active and driving a DSI display.
+ * Preserve DPOUNIT_CLOCK_GATE_DISABLE to avoid the pipe getting stuck
+ * (and never recovering) in this case. intel_dsi_post_disable() will
+ * clear it when we turn off the display.
+ */
+ val = I915_READ(DSPCLK_GATE_D);

* Disable trickle feed and enable pnd deadline calculation