Re: [PATCH] drm/i915 : Restore PWM_GRANULARITY after resume

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

On Thu, 08 Sep 2016, "Lee, Shawn C" <shawn.c.lee@intel.com> wrote:
> From: "Lee, Shawn C" <shawn.c.lee@intel.com>
>
> SPT_PWM_GRANULARITY (SOUTH_CHICKEN1, bit 0) controls the granularity
> (minimum increment) of the PWM backlight control counter. PWM frequency
> adjustment on 128 clock increments when this bit was 1. And 16 clock
> increments when it was 0.
>
> PWM frequency multiple octuple (from 200Hz to 1.6KHz) due to
> SPT_PWM_GRANULARITY was clear to 0 after S3. This patch save
> SOUTH_CHICKEN1 register value before suspend. And will restore
> it after i915 resume.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97486
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Reviewed-by: Cooper Chiou <cooper.chiou@intel.com>
> Reviewed-by: Wei Shun Chen <wei.shun.chang@intel.com>
> Reviewed-by: Gary C Wang <gary.c.wang@intel.com>
> Signed-off-by: Shawn Lee <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_drv.h   |    1 +
>  drivers/gpu/drm/i915/intel_panel.c |   21 +++++++++++++++++++--
>  2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 570a7ca..4c28692 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -256,6 +256,7 @@ struct intel_panel {
>  		u32 level;
>  		u32 min;
>  		u32 max;
> +		u32 pwm_granularity;

None of the fields here store register information directly. Please
don't do so here either. Make this a bool. Call it
pwm_alternate_increment or something.

>  		bool enabled;
>  		bool combination_mode;	/* gen 2/4 only */
>  		bool active_low_pwm;
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index c10e9b0..720fd5a 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -841,7 +841,17 @@ static void lpt_enable_backlight(struct intel_connector *connector)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>  	struct intel_panel *panel = &connector->panel;
> -	u32 pch_ctl1, pch_ctl2;
> +	u32 pch_ctl1, pch_ctl2, mul;
> +
> +	if (HAS_PCH_LPT(dev_priv)) {
> +		mul = I915_READ(SOUTH_CHICKEN2);
> +		mul &= ~LPT_PWM_GRANULARITY;
> +		I915_WRITE(SOUTH_CHICKEN2, mul | panel->backlight.pwm_granularity);
> +	} else {
> +		mul = I915_READ(SOUTH_CHICKEN1);
> +		mul &= ~SPT_PWM_GRANULARITY;
> +		I915_WRITE(SOUTH_CHICKEN1, mul | panel->backlight.pwm_granularity);
> +	}

It's probably safer to modify the granularity after we've ensured the
backlight is disabled below.

>  
>  	pch_ctl1 = I915_READ(BLC_PWM_PCH_CTL1);
>  	if (pch_ctl1 & BLM_PCH_PWM_ENABLE) {
> @@ -1413,7 +1423,7 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
>  {
>  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>  	struct intel_panel *panel = &connector->panel;
> -	u32 pch_ctl1, pch_ctl2, val;
> +	u32 pch_ctl1, pch_ctl2, val, mul;
>  
>  	pch_ctl1 = I915_READ(BLC_PWM_PCH_CTL1);
>  	panel->backlight.active_low_pwm = pch_ctl1 & BLM_PCH_POLARITY;
> @@ -1421,6 +1431,13 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
>  	pch_ctl2 = I915_READ(BLC_PWM_PCH_CTL2);
>  	panel->backlight.max = pch_ctl2 >> 16;
>  
> +	if (HAS_PCH_LPT(dev_priv))
> +		mul = I915_READ(SOUTH_CHICKEN2) & LPT_PWM_GRANULARITY;
> +	else
> +		mul = I915_READ(SOUTH_CHICKEN1) & SPT_PWM_GRANULARITY;
> +
> +	panel->backlight.pwm_granularity = mul;

In the function, there's a sequence of figuring out the max backlight,
please don't put this stuff in the middle of it. You can just make this
the first thing.

As follow-up, you can then use the field in spt_hz_to_pwm and
lpt_hz_to_pwm instead of re-reading the chicken bits there.

> +
>  	if (!panel->backlight.max)
>  		panel->backlight.max = get_backlight_max_vbt(connector);

-- 
Jani Nikula, Intel Open Source Technology Center
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