Re: [PATCH RESEND v4 6/6] drm/i915: Set PWM divider to match desired frequency in vbt

[Manasi Navare <manasi.d.navare@intel.com>]

On Wed, May 03, 2017 at 02:15:06AM +0000, Pandiyan, Dhinakaran wrote:
> On Tue, 2017-04-18 at 16:48 -0700, Puthikorn Voravootivat wrote:
> > Read desired PWM frequency from panel vbt and calculate the
> > value for divider in DPCD address 0x724 and 0x728 to match
> > that frequency as close as possible.
> > 
> > Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
> > ---
> >  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 56 +++++++++++++++++++++++++++
> >  1 file changed, 56 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index f99cf0a6ae44..9adc77bfb515 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -111,12 +111,60 @@ intel_dp_aux_set_dynamic_backlight_percent(struct intel_dp *intel_dp,
> >  			  dbc, sizeof(dbc));
> >  }
> >  
> > +/*
> > + * Set PWM Frequency divider to match desired frequency in vbt.
> > + * The PWM Frequency is calculated as 27Mhz / (F x P).
> > + * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
> > + *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> > + * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> > + *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> > + */
> > +static void intel_dp_aux_set_pwm_freq(struct intel_connector *connector)
> > +{
> > +	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> > +	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
> > +	int freq, fxp, f;
> > +	u8 pn, pn_min, pn_max;
> > +
> > +	/* Find desired value of (F x P)
> > +	 * Note that, if F x P is out of supported range, the maximum value or
> > +	 * minimum value will applied automatically. So no need to check that.
> > +	 */
> > +	freq = dev_priv->vbt.backlight.pwm_freq_hz;
> > +	fxp = DP_EDP_BACKLIGHT_FREQ_BASE / freq;
> 
> 
> 
> How do we know vbt.backlight.pwm_freq_hz isn't zero? Or am I missing
> something here.
> intel_panel.c: get_backlight_max_vbt() seems to do a check.
> 
> 
> -DK
>

Yes I had the exact same comment, you should check for if (!vbt.backlight.pwm_freq_hz)

Everything else looks good to me.

Manasi
 
> > +
> > +	/* Use lowest possible value of Pn to try to make F to be between 1 and
> > +	 * 255 while still in the range Pn_min and Pn_max
> > +	 */
> > +	if (!drm_dp_dpcd_readb(&intel_dp->aux,
> > +			       DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min)) {
> > +		return;
> > +	}
> > +	if (!drm_dp_dpcd_readb(&intel_dp->aux,
> > +			       DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max)) {
> > +		return;
> > +	}
> > +	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +	f = fxp / (1 << pn_min);
> > +	for (pn = pn_min; pn < pn_max && f > 255; pn++)
> > +		f /= 2;
> > +
> > +	/* Cap F to be in the range between 1 and 255. */
> > +	f = min(f, 255);
> > +	f = max(f, 1);
> > +
> > +	drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
> > +	drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET, (u8) f);
> > +}
> > +
> >  static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
> >  {
> >  	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
> >  	uint8_t dpcd_buf = 0;
> >  	uint8_t new_dpcd_buf = 0;
> >  	uint8_t edp_backlight_mode = 0;
> > +	bool freq_cap;
> >  
> >  	set_aux_backlight_enable(intel_dp, true);
> >  
> > @@ -147,10 +195,18 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
> >  		intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0, 100);
> >  	}
> >  
> > +	freq_cap = intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP;
> > +	if (freq_cap)
> > +		new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> > +
> >  	if (new_dpcd_buf != dpcd_buf) {
> >  		drm_dp_dpcd_writeb(&intel_dp->aux,
> >  			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> >  	}
> > +
> > +	if (freq_cap)
> > +		intel_dp_aux_set_pwm_freq(connector);
> > +
> >  	intel_dp_aux_set_backlight(connector, connector->panel.backlight.level);
> >  }
> >  
> 
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