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

[River Zhou]

commit bb98e72adaf9d19719aba35f802d4836f5d5176c
Author: Hans de Goede <hdegoede at redhat.com>
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
    comment

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

Signed-off-by: River Zhou <riverzhou2000 at 163.com>
---
 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)
 {
-	I915_WRITE(DSPCLK_GATE_D, VRHUNIT_CLOCK_GATE_DISABLE);
+        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);
+        val &= DPOUNIT_CLOCK_GATE_DISABLE;
+        val |= VRHUNIT_CLOCK_GATE_DISABLE;
+        I915_WRITE(DSPCLK_GATE_D, val);
 
 	/*
 	 * Disable trickle feed and enable pnd deadline calculation
-- 
2.7.4