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

[David Weinehall]

On Wed, Jul 05, 2017 at 01:03:46PM +0300, Jani Nikula wrote:
> On Tue, 04 Jul 2017, David Weinehall <david.weinehall at linux.intel.com> wrote:
> > This reverts commit ae25eceab616d16a07bcaa434b84463d58a3bdc3.
> >
> > The introduction of dynamic backlight control causes
> > Lenovo ThinkPad X1 Carbon 4th Gen to boot to a black screen;
> > presumably the backlight is off.
> 
> Oh, I thought reverting just this commit was not enough for you, based
> on the previous discussion in the patch thread. If this is enough, and
> the DPCD backlight by default works for you, I might be inclined to go
> with just defaulting to false here.

Yeah, that was indeed my experience, but I cannot reproduce that
behaviour now; disabling DBC seems to be enough to make things work.
It might be that I made some mistake in my earlier testing.

I retested now, with the following results:

Both DPCD & DBC enabled: black screen
DBC enabled, DPCD disabled: works
DBC disabled, DPCD enabled: works
DBC disabled, DPCD disabled: works

Based on my understanding of the code, DPCD backlight is required for
DBC to work, so it makes sense that disabling either of the two
makes things work (hence I don't understand how I got my earlier
result where just disabling DBC wasn't enough).

Anyhow, I'm fine with just changing the default to false.


Kind regards, David

> BR,
> Jani.
> 
> 
> >
> > Signed-off-by: David Weinehall <david.weinehall at linux.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, 1 insertion(+), 33 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> > index 88b9d3e6713a..5b5ab15d191f 100644
> > --- a/drivers/gpu/drm/i915/i915_params.c
> > +++ b/drivers/gpu/drm/i915/i915_params.c
> > @@ -65,7 +65,6 @@ 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);
> > @@ -255,7 +254,3 @@ 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 057e203e6bda..0d6cf9138dc4 100644
> > --- a/drivers/gpu/drm/i915/i915_params.h
> > +++ b/drivers/gpu/drm/i915/i915_params.h
> > @@ -67,8 +67,7 @@
> >  	func(bool, verbose_state_checks); \
> >  	func(bool, nuclear_pageflip); \
> >  	func(bool, enable_dp_mst); \
> > -	func(bool, enable_gvt); \
> > -	func(bool, enable_dbc)
> > +	func(bool, enable_gvt)
> >  
> >  #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 b25cd88fc1c5..fea161727c6e 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -173,24 +173,6 @@ 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)
> >  {
> > @@ -226,14 +208,6 @@ 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) {
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center