Some 855gm models (at least ThinkPad X40) regressed because of
commit b0cd324faed23d10d66ba6ade66579c681feef6f
Author: Jani Nikula <jani.nikula@xxxxxxxxx>
Date: Wed Nov 12 16:25:43 2014 +0200
drm/i915: don't save/restore backlight hist ctl registers
which tried to make our driver more robust by not blindly saving and
restoring registers, but it failed to take into account
commit 0eb96d6ed38430b72897adde58f5477a6b71757a
Author: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
Date: Wed Oct 14 12:33:41 2009 -0700
drm/i915: save/restore BLC histogram control reg across suspend/resume
Fix the regression by enabling hist ctl on gen2.
v2: Improved the comment.
v3: Improved the comment, again.
Reported-and-tested-by: Philipp Gesang <phg@xxxxxxxxxxxxx>
References: http://mid.gmane.org/20150623222648.GD12335@acheron
Fixes: b0cd324faed2 ("drm/i915: don't save/restore backlight hist ctl registers")
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Acked-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_reg.h | 1 +
drivers/gpu/drm/i915/intel_panel.c | 8 ++++++++
2 files changed, 9 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index fa9ccb87eb66..bf7c08b94088 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3507,6 +3507,7 @@ enum skl_disp_power_wells {
#define BLM_POLARITY_PNV (1 << 0) /* pnv only */
#define BLC_HIST_CTL (dev_priv->info.display_mmio_offset + 0x61260)
+#define BLM_HISTOGRAM_ENABLE (1 << 31)
/* New registers for PCH-split platforms. Safe where new bits show up, the
* register layout machtes with gen4 BLC_PWM_CTL[12]. */
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 7d83527f95f7..55aad2322e10 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -907,6 +907,14 @@ static void i9xx_enable_backlight(struct intel_connector *connector)
/* XXX: combine this into above write? */
intel_panel_actually_set_backlight(connector, panel->backlight.level);
+
+ /*
+ * Needed to enable backlight on some 855gm models. BLC_HIST_CTL is
+ * 855gm only, but checking for gen2 is safe, as 855gm is the only gen2
+ * that has backlight.
+ */
+ if (IS_GEN2(dev))
+ I915_WRITE(BLC_HIST_CTL, BLM_HISTOGRAM_ENABLE);
}
static void i965_enable_backlight(struct intel_connector *connector)
--
2.1.4
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