The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bb83d5fb550bb7db75b29e6342417fda2bbb691c Mon Sep 17 00:00:00 2001

From: Jani Nikula jani.nikula@intel.com Date: Fri, 8 Jan 2021 17:28:41 +0200 Subject: [PATCH] drm/i915/backlight: fix CPU mode backlight takeover on LPT MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight() functions operate directly on the hardware registers. If inverting the value is needed, using intel_panel_compute_brightness(), it should only be done in the interface between hardware registers and panel->backlight.level.

The CPU mode takeover code added in commit 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the hardware register and converts to panel->backlight.level correctly, however the value written back should remain in the hardware register "domain".

This hasn't been an issue, because GM45 machines are the only known users of i915.invert_brightness and the brightness invert quirk, and without one of them no conversion is made. It's likely nobody's ever hit the problem.

Fixes: 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.") Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Lyude Paul lyude@redhat.com Cc: stable@vger.kernel.org # v5.1+ Reviewed-by: Lyude Paul lyude@redhat.com Signed-off-by: Jani Nikula jani.nikula@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20210108152841.6944-1-jani.nik... (cherry picked from commit 0d4ced1c5bfe649196877d90442d4fd618e19153) Signed-off-by: Jani Nikula jani.nikula@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c index 9f23bac0d792..d64fce1a17cb 100644 --- a/drivers/gpu/drm/i915/display/intel_panel.c +++ b/drivers/gpu/drm/i915/display/intel_panel.c @@ -1650,16 +1650,13 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus val = pch_get_backlight(connector); else val = lpt_get_backlight(connector); - val = intel_panel_compute_brightness(connector, val); - panel->backlight.level = clamp(val, panel->backlight.min, - panel->backlight.max);

if (cpu_mode) { drm_dbg_kms(&dev_priv->drm, "CPU backlight register was enabled, switching to PCH override\n");

/* Write converted CPU PWM value to PCH override register */ - lpt_set_backlight(connector->base.state, panel->backlight.level); + lpt_set_backlight(connector->base.state, val); intel_de_write(dev_priv, BLC_PWM_PCH_CTL1, pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);

@@ -1667,6 +1664,10 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus cpu_ctl2 & ~BLM_PWM_ENABLE); }

+ val = intel_panel_compute_brightness(connector, val); + panel->backlight.level = clamp(val, panel->backlight.min, + panel->backlight.max); + return 0; }