[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 20:56:49 UTC 2017
On Tue, May 16, 2017 at 1:29 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan at intel.com> wrote:
> On Tue, 2017-05-16 at 11:07 -0700, Puthikorn Voravootivat wrote:
> >
> >
> > 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.
> >
> Not sure I got that, what's the invalid "f" case that you see with
> pn==pn_min?
>
>
> if the for loop has pn > pn_min, when pn == pn_min we will exit the loop
first
without running the f = clamp(fxp >> pn, 1, 255); in the next line.
This would fix with pn >= pn_min in for loop.
We guarantee that the break statement will be called and pn won't be pn_min
- 1
because we check (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max)
before
entering this for loop.
> > 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 makes it somewhat clear but gets confusing again.
> >
> > 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.
> >
>
> Note:
> The number of assigned or controllable bits will have the ability to
> provide full brightness control. Examples:
> •
> For 10-bit operation, 000h = 0% brightness, and 3FFh = 100% brightness.
>
> Going by the logic you stated, for a 10-bit control, the MSB and LSB
> registers have to be written FFFFh to set 100% brightness with the last
> 6 bits dropped off by the hardware.
>
> I don't like the way the spec leaves this to interpretation. Have you
> experimented with both 0x0ABC and 0xABCD for the 12-bit, BYTE_COUNT==1
> example you gave?
>
> Yes, already test with the real panel.
Here is better test case than 0xABCD
0xFFFF with 6, 12, 16 shows very bright screen with same brightness in all
case. (All 100%)
0x0FFF with 6, 12, 16 bits shows dim screen. 6 bit case is slightly dimmer
than other case.
Note that the brightness are 4.76% / 6.23% / 6.25% in 6 / 12 / 16 bits case.
You can apply this patch for easy testing
https://patchwork.kernel.org/patch/6241481/
>
> >
> >
> > 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.
>
> Sure. This patch should be good to go with answers to my questions. The
> only thing remaining would be getting an ACK from Jani for adding a new
> parameter for dynamic backlight control.
>
>
> -DK
>
> > 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
> >
> >
> >
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
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