[Intel-gfx] [PATCH v12 3/3] drm/i915: Add option to support dynamic backlight via DPCD

[David Weinehall]

On Mon, Jun 26, 2017 at 05:18:19PM +0300, David Weinehall wrote:
> On Thu, Jun 22, 2017 at 12:03:39PM -0700, Puthikorn Voravootivat wrote:
> > This patch adds option to enable dynamic backlight for eDP
> > panel that supports this feature via DPCD register and
> > set minimum / maximum brightness to 0% and 100% of the
> > normal brightness.
> 
> This patch causes a regression on my ThinkPad X1 Carbon Gen 4;
> with enable_dbc = true the backlight stays off; setting i915.enable_dbc=0
> on boot makes things work properly again.

Some more testing indicates that while i915.enable_dbc=0 solves the
initial issue of backlight not coming on, it's not enough--after
suspend/resume the backlight stays off.

Passing i915.enable_dpcd_backlight=0 seems to work both for the initial
case of backlight not coming on at boot, and the issue with backlight
not coming on after suspend/resume.

So:

DBC:1, DPCD: -1: blank screen on boot
DBC:0, DPCD: -1: screen OK on boot, blank after suspend/resume
DBC:1, DPCD:  0: screen OK on boot, screen OK after suspend/resume
DBC:0, DPCD:  0: screen OK on boot, screen OK after suspend/resume

So it seems that at least for the ThinkPad X1 Carbon Gen 4 (possibly
limited to the 2560x1440 model) DPCD backlight isn't supported.

Or possibly something is wrong with the DPCD backlight patch.

> > Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> > Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_params.c            |  5 +++++
> >  drivers/gpu/drm/i915/i915_params.h            |  3 ++-
> >  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 26 ++++++++++++++++++++++++++
> >  3 files changed, 33 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> > index 5b5ab15d191f..88b9d3e6713a 100644
> > --- a/drivers/gpu/drm/i915/i915_params.c
> > +++ b/drivers/gpu/drm/i915/i915_params.c
> > @@ -65,6 +65,7 @@ struct i915_params i915 __read_mostly = {
> >  	.inject_load_failure = 0,
> >  	.enable_dpcd_backlight = -1,
> >  	.enable_gvt = false,
> > +	.enable_dbc = true,
> >  };
> >  
> >  module_param_named(modeset, i915.modeset, int, 0400);
> > @@ -254,3 +255,7 @@ MODULE_PARM_DESC(enable_dpcd_backlight,
> >  module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
> >  MODULE_PARM_DESC(enable_gvt,
> >  	"Enable support for Intel GVT-g graphics virtualization host support(default:false)");
> > +
> > +module_param_named_unsafe(enable_dbc, i915.enable_dbc, bool, 0600);
> > +MODULE_PARM_DESC(enable_dbc,
> > +	"Enable support for dynamic backlight control (default:true)");
> > diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> > index 0d6cf9138dc4..057e203e6bda 100644
> > --- a/drivers/gpu/drm/i915/i915_params.h
> > +++ b/drivers/gpu/drm/i915/i915_params.h
> > @@ -67,7 +67,8 @@
> >  	func(bool, verbose_state_checks); \
> >  	func(bool, nuclear_pageflip); \
> >  	func(bool, enable_dp_mst); \
> > -	func(bool, enable_gvt)
> > +	func(bool, enable_gvt); \
> > +	func(bool, enable_dbc)
> >  
> >  #define MEMBER(T, member) T member
> >  struct i915_params {
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index fea161727c6e..b25cd88fc1c5 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -173,6 +173,24 @@ static bool intel_dp_aux_set_pwm_freq(struct intel_connector *connector)
> >  	return true;
> >  }
> >  
> > +/*
> > +* Set minimum / maximum dynamic brightness percentage. This value is expressed
> > +* as the percentage of normal brightness in 5% increments.
> > +*/
> > +static bool
> > +intel_dp_aux_set_dynamic_backlight_percent(struct intel_dp *intel_dp,
> > +					   u32 min, u32 max)
> > +{
> > +	u8 dbc[] = { DIV_ROUND_CLOSEST(min, 5), DIV_ROUND_CLOSEST(max, 5) };
> > +
> > +	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET,
> > +			  dbc, sizeof(dbc)) < 0) {
> > +		DRM_DEBUG_KMS("Failed to write aux DBC brightness level\n");
> > +		return false;
> > +	}
> > +	return true;
> > +}
> > +
> >  static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
> >  					  const struct drm_connector_state *conn_state)
> >  {
> > @@ -208,6 +226,14 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
> >  		if (intel_dp_aux_set_pwm_freq(connector))
> >  			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> >  
> > +	if (i915.enable_dbc &&
> > +	    (intel_dp->edp_dpcd[2] & DP_EDP_DYNAMIC_BACKLIGHT_CAP)) {
> > +		if(intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0, 100)) {
> > +			new_dpcd_buf |= DP_EDP_DYNAMIC_BACKLIGHT_ENABLE;
> > +			DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> > +		}
> > +	}
> > +
> >  	if (new_dpcd_buf != dpcd_buf) {
> >  		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> >  			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
> > -- 
> > 2.13.1.611.g7e3b11ae1-goog
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx