[Intel-gfx] [PATCH v7 9/9] drm/i915: Set PWM divider to match desired frequency in vbt
Puthikorn Voravootivat
puthik at chromium.org
Sat May 13 00:31:10 UTC 2017
On Fri, May 12, 2017 at 5:12 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan at intel.com> wrote:
> On Thu, 2017-05-11 at 16:02 -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 is still within 25%
> > of the desired frequency.
>
> I read a few eDP panel data sheets, the PWM frequencies all start from
> ~200Hz. If the VBT chooses this lowest value to allow for more
> brightness control, and then this patch lowers the value by another 25%,
> we'll end up below the panel allowed PWM frequency.
>
> In fact, one of the systems I checked had PWM frequency as 200Hz in VBT
> and the panel datasheet also had PWM frequency range starting from
> 200Hz. Have you considered this case?
>
> The spec said "A given LCD panel typically has a limited range of
backlight frequency capability.
To limit the programmable frequency range, limitations are placed on the
allowable total divider ratio with the Sink device"
So I think it should be auto cap to 200Hz in this case.
> -DK
> >
> > Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> > ---
> > drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 81
> +++++++++++++++++++++++++++
> > 1 file changed, 81 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index 0b48851013cc..6f10a2f1ab76 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -113,12 +113,86 @@ 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 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, fxp_min, fxp_max, fxp_actual, f = 1;
> > + 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;
> > + }
> > +
> > + fxp = 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
> > + * - Effective frequency is within 25% of desired frequency.
> > + */
> > + 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;
> > + }
> > + 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;
> > + }
> > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +
> > + fxp_min = fxp * 3 / 4;
> > + fxp_max = fxp * 5 / 4;
>
> You are allowing fxp between +/- 25% of the actual. This isn't same as
> the "Effective frequency is within 25% of desired frequency." right? The
> frequency can vary between -20% and +33%.
>
> You are right.
You want me to change commit message to reflect this or change the code to
match the commit message?
>
> > + if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> > + DRM_DEBUG_KMS("VBT defined backlight frequency out of
> range\n");
> > + return;
> > + }
> > +
> > + for (pn = pn_max; pn > pn_min; pn--) {
> > + f = clamp(fxp >> 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;
> > + }
> > + 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;
> > + }
> > +}
> > +
> > 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;
> >
> > if (drm_dp_dpcd_readb(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) !=
> 1) {
> > @@ -151,6 +225,10 @@ static void intel_dp_aux_enable_backlight(struct
> intel_connector *connector)
> > DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> > }
> >
> > + 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) {
> > if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf)
> < 0) {
> > @@ -158,6 +236,9 @@ static void intel_dp_aux_enable_backlight(struct
> intel_connector *connector)
> > }
> > }
> >
> > + if (freq_cap)
> > + intel_dp_aux_set_pwm_freq(connector);
> > +
> > set_aux_backlight_enable(intel_dp, true);
> > intel_dp_aux_set_backlight(connector, connector->panel.backlight.
> level);
> > }
>
>
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