[Intel-gfx] [PATCH v7 9/9] drm/i915: Set PWM divider to match desired frequency in vbt
Puthikorn Voravootivat
puthik at chromium.org
Tue May 16 00:43:26 UTC 2017
On Mon, May 15, 2017 at 4:07 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan at intel.com> wrote:
> On Fri, 2017-05-12 at 17:31 -0700, Puthikorn Voravootivat wrote:
> >
> >
> >
> > 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?
>
> I am okay with fixing the comment and commit message. Is the 25%
> arbitrary or based on the distances between the possible values? Please
> make a note in the comment if it's the former.
>
>
> > > + 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--) {
>
> Is there a reason this is not pn >= pn_min?
>
This is bug because f value will be incorrect in the case that pn == pn_min.
Thanks for catching this.
>
> > > + 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");
>
>
> If the number of brightness control bits are changing, the max.
> brightness value changes too.
>
> Please see intel_dp_aux_setup_backlight().
>
> I think this is fine because
- intel_dp_aux_setup_backlight() will
called intel_dp_aux_enable_backlight() which
called intel_dp_aux_set_pwm_freq() first before determine the max
brightness value.
- Also, the panel I tested does not change BACKLIGHT_BRIGHTNESS_BYTE_COUNT
when changing the frequency.
>
>
> > > + 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);
> > > }
> >
> >
> >
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
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