Some 855gm models (at least ThinkPad X40) regressed because of
commit b0cd324faed23d10d66ba6ade66579c681feef6f
Author: Jani Nikula <jani.nik...@intel.com>
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 <jbar...@virtuousgeek.org>
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.
Reported-and-tested-by: Philipp Gesang <p...@phi-gamma.net>
References: http://mid.gmane.org/20150623222648.GD12335@acheron
Fixes: b0cd324faed2 ("drm/i915: don't save/restore backlight hist ctl
registers")
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Cc: sta...@vger.kernel.org
Acked-by: Chris Wilson <ch...@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nik...@intel.com>
---
drivers/gpu/drm/i915/i915_reg.h | 1 +
drivers/gpu/drm/i915/intel_panel.c | 7 +++++++
2 files changed, 8 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..a55477c59559 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -907,6 +907,13 @@ 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. 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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