Re: [PATCH v10 3/3] drm/i915: Set PWM divider to match desired frequency in vbt

[Puthikorn Voravootivat <puthik@chromium.org>]

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On Tue, May 30, 2017 at 8:40 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan@intel.com> wrote:

> The patch looks good overall, it would have been easier to merge if
> you'd sent this as the first patch in this version. Some comments
> inline.
>
>
> Will re-order to make this the first patch in the next version.

>
> On Fri, 2017-05-26 at 18:42 -0700, Puthikorn Voravootivat wrote:
> > Read desired PWM frequency from panel vbt and calculate the
> > value for divider in DPCD address 0x724 and 0x728 to have
> > as many bits as possible for PWM duty cyle for granularity of
> > brightness adjustment while the frequency divisor is still
> > within 25% of the desired value.
> >
> > Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
> > ---
> >  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 79
> +++++++++++++++++++++++++++
> >  1 file changed, 79 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index f55af41ce3bd..a8d485a29f29 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -116,6 +116,81 @@ intel_dp_aux_set_dynamic_backlight_percent(struct
> intel_dp *intel_dp,
> >       }
> >  }
> >
> > +/*
> > + * 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 int 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, fxp_min, fxp_max, fxp_actual, f = 1;
>
> nit: unnecessary initialization for f?
>
No. We only set f in for (pn = pn_max; pn >= pn_min; pn--) but compiler
wouldn't
know that pn_max  >= pn_min so f might be uninitialized.


> > +     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;
> > +     DRM_DEBUG_KMS("VBT defined backlight frequency %u Hz\n", freq);
> > +     if (!freq) {
> > +             DRM_DEBUG_KMS("Use panel default backlight frequency\n");
> > +             return -1;
> > +     }
> > +
> > +     fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ),
> freq);
> > +
> > +     /* Use highest possible value of Pn for more granularity of
> brightness
> > +      * adjustment while satifying the conditions below.
> > +      * - Pn is in the range of Pn_min and Pn_max
> > +      * - F is in the range of 1 and 255
> > +      * - FxP is within 25% of desired value.
> > +      *   Note: 25% is arbitrary value and may need some tweak.
> > +      */
> > +     if (drm_dp_dpcd_readb(&intel_dp->aux,
> > +                            DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min)
> != 1) {
> > +             DRM_DEBUG_KMS("Failed to read pwmgen bit count cap min\n");
> > +             return -EIO;
>
> The error numbers are not propagated outside, so I don't see a real need
> for them. bool should suffice.
>
> Sure.

>
> > +     }
> > +     if (drm_dp_dpcd_readb(&intel_dp->aux,
> > +                            DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max)
> != 1) {
> > +             DRM_DEBUG_KMS("Failed to read pwmgen bit count cap max\n");
> > +             return -EIO;
> > +     }
> > +     pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +     pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +
> > +     fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> > +     fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> > +     if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> > +             DRM_DEBUG_KMS("VBT defined backlight frequency out of
> range\n");
> > +             return -ERANGE;
> > +     }
> > +
> > +     for (pn = pn_max; pn >= pn_min; pn--) {
> > +             f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> > +             fxp_actual = f << pn;
> > +             if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> > +                     break;
> > +     }
> > +
> > +     if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > +                            DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
> > +             DRM_DEBUG_KMS("Failed to write aux pwmgen bit count\n");
> > +             return -EIO;
> > +     }
> > +     if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > +                            DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
> > +             DRM_DEBUG_KMS("Failed to write aux backlight freq\n");
> > +             return -EIO;
> > +     }
> > +     return 0;
> > +}
> > +
> >  static void intel_dp_aux_enable_backlight(struct intel_connector
> *connector)
> >  {
> >       struct intel_dp *intel_dp = enc_to_intel_dp(&connector->
> encoder->base);
> > @@ -152,6 +227,10 @@ static void intel_dp_aux_enable_backlight(struct
> intel_connector *connector)
> >               DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> >       }
> >
> > +     if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> > +             if (!intel_dp_aux_set_pwm_freq(connector))
>
> nit: This doesn't read right to me, looking at the function name it
> seems like you are proceeding when it failed.
>
> OK.

>
> > +                     new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_
> ENABLE;
> > +
> >       if (new_dpcd_buf != dpcd_buf) {
> >               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> >                       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf)
> < 0) {
>
>

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