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Message-ID: <87eejw765m.fsf@intel.com>
Date: Fri, 11 Dec 2020 16:45:41 +0200
From: Jani Nikula <jani.nikula@...el.com>
To: Lyude Paul <lyude@...hat.com>, dri-devel@...ts.freedesktop.org,
nouveau@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org
Cc: Dave Airlie <airlied@...il.com>, greg.depoire@...il.com,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Ville Syrjälä <ville.syrjala@...ux.intel.com>,
Imre Deak <imre.deak@...el.com>,
José Roberto de Souza <jose.souza@...el.com>,
Manasi Navare <manasi.d.navare@...el.com>,
Sean Paul <seanpaul@...omium.org>,
Lucas De Marchi <lucas.demarchi@...el.com>,
Juha-Pekka Heikkila <juhapekka.heikkila@...il.com>,
Dave Airlie <airlied@...hat.com>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 3/5] drm/i915/dp: Remove redundant AUX backlight frequency calculations
On Wed, 09 Dec 2020, Lyude Paul <lyude@...hat.com> 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.
This isn't a full review, just something I spotted so far. Please see
inline.
BR,
Jani.
>
> 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 | 64 ++++++-------------
> 2 files changed, 19 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 5bc5bfbc4551..133c9cb742a7 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -259,6 +259,7 @@ struct intel_panel {
>
> /* DPCD backlight */
> u8 pwmgen_bit_count;
> + u8 pwm_freq_pre_divider;
>
> struct backlight_device *device;
>
> 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 4fd536801b14..94ce5ca1affa 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -129,50 +129,6 @@ intel_dp_aux_set_backlight(const struct drm_connector_state *conn_state, u32 lev
> }
> }
>
> -/*
> - * 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_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.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_enable_backlight(const struct intel_crtc_state *crtc_state,
> const struct drm_connector_state *conn_state)
> {
> @@ -213,9 +169,13 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
> break;
> }
>
> - if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> - if (intel_dp_aux_set_pwm_freq(connector))
> + if (panel->backlight.pwm_freq_pre_divider) {
> + if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
> + panel->backlight.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,
> @@ -236,6 +196,14 @@ static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old
> 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_calc_max_backlight(struct intel_connector *connector)
> {
> struct drm_i915_private *i915 = to_i915(connector->base.dev);
> @@ -287,8 +255,10 @@ static u32 intel_dp_aux_calc_max_backlight(struct intel_connector *connector)
> 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");
> @@ -309,7 +279,9 @@ static u32 intel_dp_aux_calc_max_backlight(struct intel_connector *connector)
> "Failed to write aux pwmgen bit count\n");
> return max_backlight;
> }
> +
> panel->backlight.pwmgen_bit_count = pn;
> + panel->backlight.pwm_freq_pre_divider = f;
This should be wrapped in
if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
but you do it in the next patch, so this patch is a bit broken.
>
> max_backlight = (1 << pn) - 1;
--
Jani Nikula, Intel Open Source Graphics Center
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