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drm/i915/dpcd_bl: Remove redundant AUX backlight frequency calculations
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Noticed this while moving all of the VESA backlight code in i915 over to
DRM helpers: it would appear that we calculate the frequency value we want
to write to DP_EDP_BACKLIGHT_FREQ_SET twice even though this value never
actually changes during runtime. So, let's simplify things by just caching
this value in intel_panel.backlight, and re-writing it as-needed.

Changes since v1:
* Wrap panel->backlight.edp.vesa.pwm_freq_pre_divider in
  DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP check - Jani

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
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514181504.565252-2-lyude@redhat.com
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Lyude Paul committed Jun 9, 2021
1 parent 241a9e2 commit 4154fa0
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Showing 2 changed files with 20 additions and 46 deletions.
1 change: 1 addition & 0 deletions drivers/gpu/drm/i915/display/intel_display_types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -311,6 +311,7 @@ struct intel_panel {
union {
struct {
u8 pwmgen_bit_count;
u8 pwm_freq_pre_divider;
} vesa;
struct {
bool sdr_uses_aux;
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65 changes: 19 additions & 46 deletions drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -373,50 +373,6 @@ intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
}
}

/*
* 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 bool intel_dp_aux_vesa_set_pwm_freq(struct intel_connector *connector)
{
struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
struct intel_dp *intel_dp = intel_attached_dp(connector);
const u8 pn = connector->panel.backlight.edp.vesa.pwmgen_bit_count;
int freq, fxp, f, fxp_actual, fxp_min, fxp_max;

freq = dev_priv->vbt.backlight.pwm_freq_hz;
if (!freq) {
drm_dbg_kms(&dev_priv->drm,
"Use panel default backlight frequency\n");
return false;
}

fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
fxp_actual = f << pn;

/* 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 > fxp_actual || fxp_actual > fxp_max) {
drm_dbg_kms(&dev_priv->drm, "Actual frequency out of range\n");
return false;
}

if (drm_dp_dpcd_writeb(&intel_dp->aux,
DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
drm_dbg_kms(&dev_priv->drm,
"Failed to write aux backlight freq\n");
return false;
}
return true;
}

static void
intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
const struct drm_connector_state *conn_state, u32 level)
Expand Down Expand Up @@ -459,9 +415,13 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
break;
}

if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
if (intel_dp_aux_vesa_set_pwm_freq(connector))
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,
Expand All @@ -482,6 +442,14 @@ static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state
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);
Expand Down Expand Up @@ -533,8 +501,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
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");
Expand All @@ -555,7 +525,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
"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;

Expand Down

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