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Message-ID: <87wnrdpfe2.fsf@intel.com>
Date: Tue, 01 Jun 2021 22:13:25 +0300
From: Jani Nikula <jani.nikula@...el.com>
To: Rodrigo Vivi <rodrigo.vivi@...el.com>,
Lyude Paul <lyude@...hat.com>
Cc: intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
nouveau@...ts.freedesktop.org,
Rajeev Nandan <rajeevny@...eaurora.org>,
greg.depoire@...il.com, David Airlie <airlied@...ux.ie>,
Lucas De Marchi <lucas.demarchi@...el.com>,
open list <linux-kernel@...r.kernel.org>,
Anshuman Gupta <anshuman.gupta@...el.com>,
Uma Shankar <uma.shankar@...el.com>,
Sean Paul <seanpaul@...omium.org>,
Dave Airlie <airlied@...hat.com>,
Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
Subject: Re: [PATCH v6 1/9] drm/i915/dpcd_bl: Remove redundant AUX backlight frequency calculations
On Fri, 21 May 2021, Rodrigo Vivi <rodrigo.vivi@...el.com> wrote:
> On Fri, May 14, 2021 at 02:14:55PM -0400, Lyude Paul wrote:
>> 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
>
> This looks okay to me now... Jani, agree?
Reviewed-by: Jani Nikula <jani.nikula@...el.com>
>
>>
>> Signed-off-by: Lyude Paul <lyude@...hat.com>
>> Cc: Jani Nikula <jani.nikula@...el.com>
>> Cc: Dave Airlie <airlied@...il.com>
>> Cc: greg.depoire@...il.com
>> ---
>> .../drm/i915/display/intel_display_types.h | 1 +
>> .../drm/i915/display/intel_dp_aux_backlight.c | 65 ++++++-------------
>> 2 files changed, 20 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
>> index 9c0adfc60c6f..7054a37363fb 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
>> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
>> @@ -311,6 +311,7 @@ struct intel_panel {
>> union {
>> struct {
>> u8 pwmgen_bit_count;
>> + u8 pwm_freq_pre_divider;
>> } 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 8e9ac9ba1d38..68bfe50ada59 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
>> @@ -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)
>> @@ -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,
>> @@ -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);
>> @@ -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");
>> @@ -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;
>>
>> --
>> 2.31.1
>>
--
Jani Nikula, Intel Open Source Graphics Center
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