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Commit 2059ac3b authored by Jani Nikula's avatar Jani Nikula
Browse files

drm/i915: fix backlight after resume on 855gm 



Some 855gm models (at least ThinkPad X40) regressed because of

commit b0cd324f
Author: Jani Nikula <jani.nikula@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 0eb96d6e
Author: Jesse Barnes <jbarnes@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.

v3: Improved the comment, again.

Reported-and-tested-by: default avatarPhilipp Gesang <phg@phi-gamma.net>
References: http://mid.gmane.org/20150623222648.GD12335@acheron


Fixes: b0cd324f ("drm/i915: don't save/restore backlight hist ctl registers")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Acked-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
parent 8b572a42

drivers/gpu/drm/i915/i915_reg.h

+1 −0
Original line number Diff line number Diff line
@@ -3491,6 +3491,7 @@ 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]. */

drivers/gpu/drm/i915/intel_panel.c

+8 −0
Original line number Diff line number Diff line
@@ -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)