Re: [PATCH 6/6] drm/i915: set the backlight panel delays registers to 1

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 19 Dec 2013, Paulo Zanoni <przanoni@gmail.com> wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
>
> Because we already do the wait in software: see
> ironlake_wait_backlight_on and ironlake_edp_wait_backlight_off.
>
> For the "backlight on" delay, even BSpec says we need to program 0x1
> to PP_ON_DELAYS 12:0.
>
> For the "backlight off" delay, if we don't do the same thing, when we
> call ironlake_wait_panel_off we'll end up waiting for the it again.
>
> On my machine the off delay is 200ms, so we save this amount of time
> whenever we disable the panel (e.g, suspend).

Whoa. This appears to fix an eDP black screen with 24->18 bpp dithering:

https://bugs.freedesktop.org/show_bug.cgi?id=73567#c21

Jani.


>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 69d8f1c..90ff059 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3535,10 +3535,17 @@ intel_dp_init_panel_power_sequencer_registers(struct drm_device *dev,
>  		pp_div_reg = VLV_PIPE_PP_DIVISOR(pipe);
>  	}
>  
> -	/* And finally store the new values in the power sequencer. */
> +	/*
> +	 * And finally store the new values in the power sequencer. The
> +	 * backlight delays are set to 1 because we do manual waits on them. For
> +	 * T8, even BSpec recommends doing it. For T9, if we don't do this,
> +	 * we'll end up waiting for the backlight off delay twice: once when we
> +	 * do the manual sleep, and once when we disable the panel and wait for
> +	 * the PP_STATUS bit to become zero.
> +	 */
>  	pp_on = (seq->t1_t3 << PANEL_POWER_UP_DELAY_SHIFT) |
> -		(seq->t8 << PANEL_LIGHT_ON_DELAY_SHIFT);
> -	pp_off = (seq->t9 << PANEL_LIGHT_OFF_DELAY_SHIFT) |
> +		(1 << PANEL_LIGHT_ON_DELAY_SHIFT);
> +	pp_off = (1 << PANEL_LIGHT_OFF_DELAY_SHIFT) |
>  		 (seq->t10 << PANEL_POWER_DOWN_DELAY_SHIFT);
>  	/* Compute the divisor for the pp clock, simply match the Bspec
>  	 * formula. */
> -- 
> 1.8.3.1
>
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-- 
Jani Nikula, Intel Open Source Technology Center