The patch looks good overall, it would have been easier to merge if
you'd sent this as the first patch in this version. Some comments
inline.
On Fri, 2017-05-26 at 18:42 -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 divisor is still
> within 25% of the desired value.
>
> Signed-off-by: Puthikorn Voravootivat <puthik@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 79 +++++++++++++++++++++++++++
> 1 file changed, 79 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index f55af41ce3bd..a8d485a29f29 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -116,6 +116,81 @@ 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 int 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;
nit: unnecessary initialization for f?
> + 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 -1;
> + }
> +
> + 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_DEBUG_KMS("Failed to read pwmgen bit count cap min\n");
> + return -EIO;
The error numbers are not propagated outside, so I don't see a real need
for them. bool should suffice.
> + }
> + 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 -EIO;
> + }
> + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> + 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("VBT defined backlight frequency out of range\n");
> + return -ERANGE;
> + }
> +
> + 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;
> + }
> +
> + 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");
> + return -EIO;
> + }
> + 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 -EIO;
> + }
> + return 0;
> +}
> +
> static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
> {
> struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
> @@ -152,6 +227,10 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
> DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> }
>
> + if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> + if (!intel_dp_aux_set_pwm_freq(connector))
nit: This doesn't read right to me, looking at the function name it
seems like you are proceeding when it failed.
> + 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) {
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