Re: [RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers

From: Lyude Paul <lyude@redhat.com>
To: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
	intel-gfx@lists.freedesktop.org,
	Lucas De Marchi <lucas.demarchi@intel.com>,
	Anshuman Gupta <anshuman.gupta@intel.com>,
	Jani Nikula <jani.nikula@intel.com>,
	David Airlie <airlied@linux.ie>,
	open list <linux-kernel@vger.kernel.org>,
	greg.depoire@gmail.com, Uma Shankar <uma.shankar@intel.com>,
	Sean Paul <seanpaul@chromium.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Aaron Ma <aaron.ma@canonical.com>,
	Dave Airlie <airlied@redhat.com>
Subject: Re: [RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers
Date: Wed, 03 Feb 2021 16:29:39 -0500	[thread overview]
Message-ID: <a726ea964f3355a44d7ab4bc5ae4c5ec2e79847d.camel@redhat.com> (raw)
In-Reply-To: <20210203205854.GA302863@intel.com>

On Wed, 2021-02-03 at 15:58 -0500, Rodrigo Vivi wrote:
> On Mon, Jan 25, 2021 at 07:10:30PM -0500, Lyude Paul wrote:
> > Since we're about to implement eDP backlight support in nouveau using the
> > standard protocol from VESA, we might as well just take the code that's
> > already written for this and move it into a set of shared DRM helpers.
> > 
> > Note that these helpers are intended to handle DPCD related backlight
> > control bits such as setting the brightness level over AUX, probing the
> > backlight's TCON, enabling/disabling the backlight over AUX if supported,
> > etc. Any PWM-related portions of backlight control are explicitly left up
> > to the driver, as these will vary from platform to platform.
> > 
> > The only exception to this is the calculation of the PWM frequency
> > pre-divider value. This is because the only platform-specific information
> > required for this is the PWM frequency of the panel, which the driver is
> > expected to provide if available. The actual algorithm for calculating this
> > value is standard and is defined in the eDP specification from VESA.
> > 
> > Note that these helpers do not yet implement the full range of features
> > the VESA backlight interface provides, and only provide the following
> > functionality (all of which was already present in i915's DPCD backlight
> > support):
> 
> This is definitely a good move.
> 
> Also the functions are well defined and well documented.
> 
> I noticed it wouldn't be straightforward, but I was wondering if it is
> possible to make the change in 2 steps (at least):
> 1. modify i915 code in place to match new functions
> 2. move to drm adding the documentation, proper returns etc....
> 
> I couldn't get a good sense of the changes around DPCD mode for instance.

Good point - yeah I can try to do that ASAP

> 
> > 
> > * Basic control of brightness levels
> > * Basic probing of backlight capabilities
> > * Helpers for enabling and disabling the backlight
> > 
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Dave Airlie <airlied@gmail.com>
> > Cc: greg.depoire@gmail.com
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c               | 332 ++++++++++++++++++
> >  .../drm/i915/display/intel_display_types.h    |   3 +-
> >  .../drm/i915/display/intel_dp_aux_backlight.c | 288 ++-------------
> >  include/drm/drm_dp_helper.h                   |  48 +++
> >  4 files changed, 413 insertions(+), 258 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index eedbb48815b7..04cb2b6970a8 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -3082,3 +3082,335 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct
> > drm_dp_aux *aux, u8 color_spc)
> >         return 0;
> >  }
> >  EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
> > +
> > +/**
> > + * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel
> > via AUX
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + * @level: The brightness level to set
> > + *
> > + * Sets the brightness level of an eDP panel's backlight. Note that the
> > panel's backlight must
> > + * already have been enabled by the driver by calling
> > drm_edp_backlight_enable().
> > + *
> > + * Returns: %0 on success, negative error code on failure
> > + */
> > +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                               u16 level)
> > +{
> > +       int ret;
> > +       u8 buf[2] = { 0 };
> > +
> > +       if (bl->lsb_reg_used) {
> > +               buf[0] = (level & 0xFF00) >> 8;
> > +               buf[1] = (level & 0x00FF);
> > +       } else {
> > +               buf[0] = level;
> > +       }
> > +
> > +       ret = drm_dp_dpcd_write(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf,
> > sizeof(buf));
> > +       if (ret != sizeof(buf)) {
> > +               DRM_ERROR("%s: Failed to write aux backlight level: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_set_level);
> > +
> > +static int
> > +drm_edp_backlight_set_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            bool enable)
> > +{
> > +       int ret;
> > +       u8 buf;
> > +
> > +       /* The panel uses something other then DPCD for enabling it's
> > backlight */
> > +       if (!bl->aux_enable)
> > +               return 0;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, &buf);
> > +       if (ret != 1) {
> > +               DRM_ERROR("%s: Failed to read eDP display control register:
> > %d\n", aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +       if (enable)
> > +               buf |= DP_EDP_BACKLIGHT_ENABLE;
> > +       else
> > +               buf &= ~DP_EDP_BACKLIGHT_ENABLE;
> > +
> > +       ret = drm_dp_dpcd_writeb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, buf);
> > +       if (ret != 1) {
> > +               DRM_ERROR("%s: Failed to write eDP display control register:
> > %d\n", aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +/**
> > + * drm_edp_backlight_enable() - Enable an eDP panel's backlight using DPCD
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + * @level: The initial backlight level to set via AUX, if there is one
> > + *
> > + * This function handles enabling DPCD backlight controls on a panel over
> > DPCD, while additionally
> > + * restoring any important backlight state such as the given backlight
> > level, the brightness byte
> > + * count, backlight frequency, etc.
> > + *
> > + * Note that certain panels, while supporting brightness level controls
> > over DPCD, may not support
> > + * having their backlights enabled via the standard
> > %DP_EDP_DISPLAY_CONTROL_REGISTER. On such panels
> > + * &drm_edp_backlight_info.aux_enable will be set to %false, this function
> > will skip the step of
> > + * programming the %DP_EDP_DISPLAY_CONTROL_REGISTER, and the driver must
> > perform the required
> > + * implementation specific step for enabling the backlight after calling
> > this function.
> > + *
> > + * Returns: %0 on success, negative error code on failure.
> > + */
> > +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            const u16 level)
> > +{
> > +       int ret;
> > +       u8 dpcd_buf, new_dpcd_buf;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > &dpcd_buf);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       new_dpcd_buf = dpcd_buf;
> > +
> > +       if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) !=
> > DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > +               new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > +
> > +               ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl-
> > >pwmgen_bit_count);
> > +               if (ret != 1)
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit
> > count: %d\n",
> > +                                     aux->name, ret);
> > +       }
> > +
> > +       if (bl->pwm_freq_pre_divider) {
> > +               ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_FREQ_SET, bl-
> > >pwm_freq_pre_divider);
> > +               if (ret != 1)
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux backlight
> > frequency: %d\n",
> > +                                     aux->name, ret);
> > +               else
> > +                       new_dpcd_buf |=
> > DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> > +       }
> > +
> > +       if (new_dpcd_buf != dpcd_buf) {
> > +               ret = drm_dp_dpcd_writeb(aux,
> > DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> > +               if (ret != 1) {
> > +                       DRM_DEBUG_KMS("%s: Failed to write aux backlight
> > mode: %d\n",
> > +                                     aux->name, ret);
> > +                       return ret < 0 ? ret : -EIO;
> > +               }
> > +       }
> > +
> > +       ret = drm_edp_backlight_set_level(aux, bl, level);
> > +       if (ret < 0)
> > +               return ret;
> > +       ret = drm_edp_backlight_set_enable(aux, bl, true);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_enable);
> > +
> > +/**
> > + * drm_edp_backlight_disable() - Disable an eDP backlight using DPCD, if
> > supported
> > + * @aux: The DP AUX channel to use
> > + * @bl: Backlight capability info from drm_edp_backlight_init()
> > + *
> > + * This function handles disabling DPCD backlight controls on a panel over
> > AUX. Note that some
> > + * panels have backlights that are enabled/disabled by other means, despite
> > having their brightness
> > + * values controlled through DPCD. On such panels
> > &drm_edp_backlight_info.aux_enable will be set to
> > + * %false, this function will become a no-op (and we will skip updating
> > + * %DP_EDP_DISPLAY_CONTROL_REGISTER), and the driver must take care to
> > perform it's own
> > + * implementation specific step for disabling the backlight.
> > + *
> > + * Returns: %0 on success or no-op, negative error code on failure.
> > + */
> > +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl)
> > +{
> > +       int ret;
> > +
> > +       ret = drm_edp_backlight_set_enable(aux, bl, false);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_disable);
> > +
> > +static inline int
> > +drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                           u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> > +{
> > +       int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> > +       int ret;
> > +       u8 pn, pn_min, pn_max;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap:
> > %d\n", aux->name, ret);
> > +               return -ENODEV;
> > +       }
> > +
> > +       pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +       bl->max = (1 << pn) - 1;
> > +       if (!driver_pwm_freq_hz)
> > +               return 0;
> > +
> > +       /*
> > +        * Set PWM Frequency divider to match desired frequency provided by
> > the driver.
> > +        * 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)
> > +        */
> > +
> > +       /* 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.
> > +        */
> > +       fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ,
> > driver_pwm_freq_hz);
> > +
> > +       /* 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.
> > +        */
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN,
> > &pn_min);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap min:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX,
> > &pn_max);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap max:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +       pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > +
> > +       /* Ensure frequency is within 25% of desired value */
> > +       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("%s: Driver defined backlight frequency (%d)
> > out of range\n",
> > +                             aux->name, driver_pwm_freq_hz);
> > +               return 0;
> > +       }
> > +
> > +       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;
> > +       }
> > +
> > +       ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count:
> > %d\n", aux->name, ret);
> > +               return 0;
> > +       }
> > +       bl->pwmgen_bit_count = pn;
> > +       bl->max = (1 << pn) - 1;
> > +
> > +       if (edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP) {
> > +               bl->pwm_freq_pre_divider = f;
> > +               DRM_DEBUG_KMS("%s: Using backlight frequency from driver
> > (%dHz)\n",
> > +                             aux->name, driver_pwm_freq_hz);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static inline int
> > +drm_edp_backlight_probe_level(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                             u8 *current_mode)
> > +{
> > +       int ret;
> > +       u8 buf[2];
> > +       u8 mode_reg;
> > +
> > +       ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > &mode_reg);
> > +       if (ret != 1) {
> > +               DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n",
> > aux->name, ret);
> > +               return ret < 0 ? ret : -EIO;
> > +       }
> > +
> > +       *current_mode = (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK);
> > +       if (*current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               int size = 1 + bl->lsb_reg_used;
> > +
> > +               ret = drm_dp_dpcd_read(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > buf, size);
> > +               if (ret != size) {
> > +                       DRM_DEBUG_KMS("%s: Failed to read backlight level:
> > %d\n", aux->name, ret);
> > +                       return ret < 0 ? ret : -EIO;
> > +               }
> > +
> > +               if (bl->lsb_reg_used)
> > +                       return (buf[0] << 8) | buf[1];
> > +               else
> > +                       return buf[0];
> > +       }
> > +
> > +       /*
> > +        * If we're not in DPCD control mode yet, the programmed brightness
> > value is meaningless and
> > +        * the driver should assume max brightness
> > +        */
> > +       return bl->max;
> > +}
> > +
> > +/**
> > + * drm_edp_backlight_init() - Probe a display panel's TCON using the
> > standard VESA eDP backlight
> > + * interface.
> > + * @aux: The DP aux device to use for probing
> > + * @bl: The &drm_edp_backlight_info struct to fill out with information on
> > the backlight
> > + * @driver_pwm_freq_hz: Optional PWM frequency from the driver in hz
> > + * @edp_dpcd: A cached copy of the eDP DPCD
> > + * @current_level: Where to store the probed brightness level
> > + * @current_mode: Where to store the currently set backlight control mode
> > + *
> > + * Initializes a &drm_edp_backlight_info struct by probing @aux for it's
> > backlight capabilities,
> > + * along with also probing the current and maximum supported brightness
> > levels.
> > + *
> > + * If @driver_pwm_freq_hz is non-zero, this will be used as the backlight
> > frequency. Otherwise, the
> > + * default frequency from the panel is used.
> > + *
> > + * Returns: %0 on success, negative error code on failure.
> > + */
> > +int
> > +drm_edp_backlight_init(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                      u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> > +                      u16 *current_level, u8 *current_mode)
> > +{
> > +       int ret;
> > +
> > +       if (edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> > +               bl->aux_enable = true;
> > +       if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > +               bl->lsb_reg_used = true;
> > +
> > +       ret = drm_edp_backlight_probe_max(aux, bl, driver_pwm_freq_hz,
> > edp_dpcd);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       ret = drm_edp_backlight_probe_level(aux, bl, current_mode);
> > +       if (ret < 0)
> > +               return ret;
> > +       *current_level = ret;
> > +
> > +       DRM_DEBUG_KMS("%s: Found backlight level=%d/%d
> > pwm_freq_pre_divider=%d mode=%x\n",
> > +                     aux->name, *current_level, bl->max, bl-
> > >pwm_freq_pre_divider, *current_mode);
> > +       DRM_DEBUG_KMS("%s: Backlight caps: pwmgen_bit_count=%d
> > lsb_reg_used=%d aux_enable=%d\n",
> > +                     aux->name, bl->pwmgen_bit_count, bl->lsb_reg_used, bl-
> > >aux_enable);
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL(drm_edp_backlight_init);
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index 8450ab8fb245..2af208f1b467 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -263,8 +263,7 @@ struct intel_panel {
> >                 /* DPCD backlight */
> >                 union {
> >                         struct {
> > -                               u8 pwmgen_bit_count;
> > -                               u8 pwm_freq_pre_divider;
> > +                               struct drm_edp_backlight_info info;
> >                         } vesa;
> >                         struct {
> >                                 bool sdr_uses_aux;
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 62294967f430..1ae14bc9e3fe 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -268,109 +268,19 @@ intel_dp_aux_hdr_setup_backlight(struct
> > intel_connector *connector, enum pipe pi
> >  }
> >  
> >  /* VESA backlight callbacks */
> > -static void set_vesa_backlight_enable(struct intel_dp *intel_dp, bool
> > enable)
> > -{
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 reg_val = 0;
> > -
> > -       /* Early return when display use other mechanism to enable
> > backlight. */
> > -       if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> > -               return;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > DP_EDP_DISPLAY_CONTROL_REGISTER,
> > -                             &reg_val) < 0) {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_DISPLAY_CONTROL_REGISTER);
> > -               return;
> > -       }
> > -       if (enable)
> > -               reg_val |= DP_EDP_BACKLIGHT_ENABLE;
> > -       else
> > -               reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
> > -
> > -       if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_EDP_DISPLAY_CONTROL_REGISTER,
> > -                              reg_val) != 1) {
> > -               drm_dbg_kms(&i915->drm, "Failed to %s aux backlight\n",
> > -                           enable ? "enable" : "disable");
> > -       }
> > -}
> > -
> > -static bool intel_dp_aux_vesa_backlight_dpcd_mode(struct intel_connector
> > *connector)
> > -{
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 mode_reg;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                             DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> > -                             &mode_reg) != 1) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to read the DPCD register 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> > -               return false;
> > -       }
> > -
> > -       return (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> > -              DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > -}
> > -
> > -/*
> > - * Read the current backlight value from DPCD register(s) based
> > - * on if 8-bit(MSB) or 16-bit(MSB and LSB) values are supported
> > - */
> >  static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector
> > *connector, enum pipe unused)
> >  {
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 read_val[2] = { 0x0 };
> > -       u16 level = 0;
> > -
> > -       /*
> > -        * If we're not in DPCD control mode yet, the programmed brightness
> > -        * value is meaningless and we should assume max brightness
> > -        */
> > -       if (!intel_dp_aux_vesa_backlight_dpcd_mode(connector))
> > -               return connector->panel.backlight.max;
> > -
> > -       if (drm_dp_dpcd_read(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > -                            &read_val, sizeof(read_val)) < 0) {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
> > -               return 0;
> > -       }
> > -       level = read_val[0];
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > -               level = (read_val[0] << 8 | read_val[1]);
> > -
> > -       return level;
> > +       return connector->panel.backlight.level;
> >  }
> >  
> > -/*
> > - * Sends the current backlight level over the aux channel, checking if its
> > using
> > - * 8-bit or 16 bit value (MSB and LSB)
> > - */
> >  static void
> > -intel_dp_aux_vesa_set_backlight(const struct drm_connector_state
> > *conn_state,
> > -                               u32 level)
> > +intel_dp_aux_vesa_set_backlight(const struct drm_connector_state
> > *conn_state, u32 level)
> >  {
> >         struct intel_connector *connector = to_intel_connector(conn_state-
> > >connector);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > -       u8 vals[2] = { 0x0 };
> > -
> > -       vals[0] = level;
> > +       struct intel_panel *panel = &connector->panel;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       /* Write the MSB and/or LSB */
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> > {
> > -               vals[0] = (level & 0xFF00) >> 8;
> > -               vals[1] = (level & 0xFF);
> > -       }
> > -       if (drm_dp_dpcd_write(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> > -                             vals, sizeof(vals)) < 0) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to write aux backlight level\n");
> > -               return;
> > -       }
> > +       drm_edp_backlight_set_level(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info, level);
> >  }
> >  
> >  static void
> > @@ -378,176 +288,46 @@ intel_dp_aux_vesa_enable_backlight(const struct
> > intel_crtc_state *crtc_state,
> >                                    const struct drm_connector_state
> > *conn_state, u32 level)
> >  {
> >         struct intel_connector *connector = to_intel_connector(conn_state-
> > >connector);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >         struct intel_panel *panel = &connector->panel;
> > -       u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
> > -       u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1)
> > {
> > -               drm_dbg_kms(&i915->drm, "Failed to read DPCD register
> > 0x%x\n",
> > -                           DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> > -               return;
> > -       }
> > -
> > -       new_dpcd_buf = dpcd_buf;
> > -       edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > -
> > -       switch (edp_backlight_mode) {
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> > -               new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > -               new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > -
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                                      DP_EDP_PWMGEN_BIT_COUNT,
> > -                                      pwmgen_bit_count) < 0)
> > -                       drm_dbg_kms(&i915->drm,
> > -                                   "Failed to write aux pwmgen bit
> > count\n");
> > -
> > -               break;
> > -
> > -       /* Do nothing when it is already DPCD mode */
> > -       case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> > -       default:
> > -               break;
> > -       }
> > -
> > -       if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_EDP_BACKLIGHT_FREQ_SET,
> > -                                      panel-
> > >backlight.edp.vesa.pwm_freq_pre_divider) == 1)
> > -                       new_dpcd_buf |=
> > DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> > -               else
> > -                       drm_dbg_kms(&i915->drm, "Failed to write aux
> > backlight frequency\n");
> > -       }
> > -
> > -       if (new_dpcd_buf != dpcd_buf) {
> > -               if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) <
> > 0) {
> > -                       drm_dbg_kms(&i915->drm,
> > -                                   "Failed to write aux backlight mode\n");
> > -               }
> > -       }
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       intel_dp_aux_vesa_set_backlight(conn_state, level);
> > -       set_vesa_backlight_enable(intel_dp, true);
> > +       drm_edp_backlight_enable(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info, level);
> >  }
> >  
> >  static void intel_dp_aux_vesa_disable_backlight(const struct
> > drm_connector_state *old_conn_state,
> >                                                 u32 level)
> >  {
> > -
> >        set_vesa_backlight_enable(enc_to_intel_dp(to_intel_encoder(old_conn_st
> > ate->best_encoder)),
> > -                                 false);
> > -}
> > -
> > -/*
> > - * Compute PWM frequency divider value based off the frequency provided to
> > us by the 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 u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector
> > *connector)
> > -{
> > -       struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > -       struct intel_dp *intel_dp = intel_attached_dp(connector);
> > +       struct intel_connector *connector =
> > to_intel_connector(old_conn_state->connector);
> >         struct intel_panel *panel = &connector->panel;
> > -       u32 max_backlight = 0;
> > -       int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> > -       u8 pn, pn_min, pn_max;
> > -
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn)
> > == 1) {
> > -               pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -               max_backlight = (1 << pn) - 1;
> > -       }
> > -
> > -       /* 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 = i915->vbt.backlight.pwm_freq_hz;
> > -       drm_dbg_kms(&i915->drm, "VBT defined backlight frequency %u Hz\n",
> > -                   freq);
> > -       if (!freq) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Use panel default backlight frequency\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       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_dbg_kms(&i915->drm,
> > -                           "Failed to read pwmgen bit count cap min\n");
> > -               return max_backlight;
> > -       }
> > -       if (drm_dp_dpcd_readb(&intel_dp->aux,
> > -                             DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) !=
> > 1) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to read pwmgen bit count cap max\n");
> > -               return max_backlight;
> > -       }
> > -       pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -       pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> > -
> > -       /* Ensure frequency is within 25% of desired value */
> > -       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_dbg_kms(&i915->drm,
> > -                           "VBT defined backlight frequency out of
> > range\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       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;
> > -       }
> > -
> > -       drm_dbg_kms(&i915->drm, "Using eDP pwmgen bit count of %d\n", pn);
> > -       if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                              DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
> > -               drm_dbg_kms(&i915->drm,
> > -                           "Failed to write aux pwmgen bit count\n");
> > -               return max_backlight;
> > -       }
> > -
> > -       panel->backlight.edp.vesa.pwmgen_bit_count = pn;
> > -       if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> > -               panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
> > -
> > -       max_backlight = (1 << pn) - 1;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >  
> > -       return max_backlight;
> > +       drm_edp_backlight_disable(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info);
> >  }
> >  
> > -static int intel_dp_aux_vesa_setup_backlight(struct intel_connector
> > *connector,
> > -                                            enum pipe pipe)
> > +static int intel_dp_aux_vesa_setup_backlight(struct intel_connector
> > *connector, enum pipe pipe)
> >  {
> >         struct intel_panel *panel = &connector->panel;
> > +       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> > +       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > +       u16 current_level;
> > +       u8 current_mode;
> > +       int ret;
> >  
> > -       panel->backlight.max =
> > intel_dp_aux_vesa_calc_max_backlight(connector);
> > -       if (!panel->backlight.max)
> > -               return -ENODEV;
> > +       ret = drm_edp_backlight_init(&intel_dp->aux, &panel-
> > >backlight.edp.vesa.info,
> > +                                    i915->vbt.backlight.pwm_freq_hz,
> > intel_dp->edp_dpcd,
> > +                                    &current_level, &current_mode);
> > +       if (ret < 0)
> > +               return ret;
> >  
> > +       panel->backlight.max = panel->backlight.edp.vesa.info.max;
> >         panel->backlight.min = 0;
> > -       panel->backlight.level = intel_dp_aux_vesa_get_backlight(connector,
> > pipe);
> > -       panel->backlight.enabled =
> > intel_dp_aux_vesa_backlight_dpcd_mode(connector) &&
> > -                                  panel->backlight.level != 0;
> > +       if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> > +               panel->backlight.level = current_level;
> > +               panel->backlight.enabled = panel->backlight.level != 0;
> > +       } else {
> > +               panel->backlight.level = panel->backlight.max;
> > +               panel->backlight.enabled = false;
> > +       }
> >  
> >         return 0;
> >  }
> > @@ -558,16 +338,12 @@ intel_dp_aux_supports_vesa_backlight(struct
> > intel_connector *connector)
> >         struct intel_dp *intel_dp = intel_attached_dp(connector);
> >         struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >  
> > -       /* Check the eDP Display control capabilities registers to determine
> > if
> > -        * the panel can support backlight control over the aux channel.
> > -        *
> > -        * TODO: We currently only support AUX only backlight
> > configurations, not backlights which
> > +       /* TODO: We currently only support AUX only backlight
> > configurations, not backlights which
> >          * require a mix of PWM and AUX controls to work. In the mean time,
> > these machines typically
> >          * work just fine using normal PWM controls anyway.
> >          */
> > -       if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> > -           (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> > -           (intel_dp->edp_dpcd[2] &
> > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
> > +       if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> > +           drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
> >                 drm_dbg_kms(&i915->drm, "AUX Backlight Control
> > Supported!\n");
> >                 return true;
> >         }
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index edffd1dcca3e..1eca0b42fc45 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -1790,6 +1790,24 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE])
> >                 DP_MSA_TIMING_PAR_IGNORED;
> >  }
> >  
> > +/**
> > + * drm_edp_backlight_supported() - Check an eDP DPCD for VESA backlight
> > support
> > + * @edp_dpcd: The DPCD to check
> > + *
> > + * Note that currently this function will return %false for panels which
> > support various DPCD
> > + * backlight features but which require the brightness be set through PWM,
> > and don't support setting
> > + * the brightness level via the DPCD. This is a TODO.
> > + *
> > + * Returns: %True if @edp_dpcd indicates that VESA backlight controls are
> > supported, %false
> > + * otherwise
> > + */
> > +static inline bool
> > +drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> > +{
> > +       return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> > +               (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> > +}
> > +
> >  /*
> >   * DisplayPort AUX channel
> >   */
> > @@ -2089,6 +2107,36 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum
> > drm_dp_quirk quirk)
> >         return desc->quirks & BIT(quirk);
> >  }
> >  
> > +/**
> > + * struct drm_edp_backlight_info - Probed eDP backlight info struct
> > + * @pwmgen_bit_count: The pwmgen bit count
> > + * @pwm_freq_pre_divider: The PWM frequency pre-divider value being used
> > for this backlight, if any
> > + * @max: The maximum backlight level that may be set
> > + * @lsb_reg_used: Do we also write values to the
> > DP_EDP_BACKLIGHT_BRIGHTNESS_LSB register?
> > + * @aux_enable: Does the panel support the AUX enable cap?
> > + *
> > + * This structure contains various data about an eDP backlight, which can
> > be populated by using
> > + * drm_edp_backlight_init().
> > + */
> > +struct drm_edp_backlight_info {
> > +       u8 pwmgen_bit_count;
> > +       u8 pwm_freq_pre_divider;
> > +       u16 max;
> > +
> > +       bool lsb_reg_used : 1;
> > +       bool aux_enable : 1;
> > +};
> > +
> > +int
> > +drm_edp_backlight_init(struct drm_dp_aux *aux, struct
> > drm_edp_backlight_info *bl,
> > +                      u16 driver_pwm_freq_hz, const u8
> > edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> > +                      u16 *current_level, u8 *current_mode);
> > +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                               u16 level);
> > +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl,
> > +                            u16 level);
> > +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct
> > drm_edp_backlight_info *bl);
> > +
> >  #ifdef CONFIG_DRM_DP_CEC
> >  void drm_dp_cec_irq(struct drm_dp_aux *aux);
> >  void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
> > -- 
> > 2.29.2
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Sincerely,
   Lyude Paul (she/her)
   Software Engineer at Red Hat

Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've
asked me a question, are waiting for a review/merge on a patch, etc. and I
haven't responded in a while, please feel free to send me another email to check
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