[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 18:07:58 UTC 2017
On Mon, May 15, 2017 at 11:21 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan at intel.com> wrote:
> On Mon, 2017-05-15 at 17:43 -0700, Puthikorn Voravootivat wrote:
> >
> >
> > 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.
> >
>
> Isn't that a side-effect using the right shift operation for division?
>
The bug is just for loop that exit too soon.
Would DIV_ROUND_CLOSEST allow you to use pn_min?
>
It does not related to the point above, but DIV_ROUND_CLOSEST still
better than just using right shift. I will change to that in next version.
>
> >
> > > > + 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.
>
> The only values I see being set for max brightness are 0xFFFF and 0xFF
>
> if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> panel->backlight.max = 0xFFFF;
> else
> panel->backlight.max = 0xFF;
> I can't see where you are setting this based on Pn. Can you please point
> out? From what I understand, max should be 2^Pn.
>
>
It is suppose to be 0xFF or 0xFFFF only.
>From eDP spec:
0x702 bit 2 BACKLIGHT_BRIGHTNESS_BYTE_COUNT
0 = Indicates that the Sink device supports a 1-byte setting for backlight
brightness
1 = Indicates that the Sink device supports a 2-byte setting for the
backlight brightness
0x722 EDP_BACKLIGHT_BRIGHTNESS_MSB
The actual number of assigned bits for the backlight brightness PWM
generator is set by
field 4:0 of the EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h).
Assigned bits are allocated to the MSB of the enabled register combination
This means that if PWM_GEN_BIT_COUNT is less than 16 then the panel will
ignore
the least significant bit in EDP_BACKLIGHT_BRIGHTNESS register.
For example,
if BACKLIGHT_BRIGHTNESS_BYTE_COUNT == 1 and PWM_GEN_BIT_COUNT = 16
and EDP_BACKLIGHT_BRIGHTNESS == 0xabcd
In this case, all bits in EDP_BACKLIGHT_BRIGHTNESS will be used.
0xabcd means 0xabcd / 0xffff or (43981 / 65535) or 67.111%
if BACKLIGHT_BRIGHTNESS_BYTE_COUNT == 1 and PWM_GEN_BIT_COUNT = 12
and EDP_BACKLIGHT_BRIGHTNESS == 0xabcd
In this case, the last 4 bits will be discarded.
0xabcd means 0xabc / 0xfff or 2748 / 4095 or 67.106%
I think it should be fine to just have 8 or 16 bits of the max brightness
and let panel drop
the unneed bit to simplify the driver code.
> Also, won't this function be called every time _enable_backlight() is
> called? Isn't doing this from setup sufficient? I guess, fixing it is an
> optimization that'd be nice to have but not necessary.
>
Lets get this patch set done first. I can send in another patch after this
is go in to optimize this.
Probably need to add new member in struct drm_i915_private
> >
> >
> > > > + 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
> >
> >
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20170516/9dbe8f30/attachment-0001.html>
More information about the dri-devel
mailing list