drivers/gpu/drm/i915/intel_dp_aux_backlight.c - third_party/linux - Git at Google

 /*
  * Copyright © 2015 Intel Corporation
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  * and/or sell copies of the Software, and to permit persons to whom the
  * Software is furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice (including the next
  * paragraph) shall be included in all copies or substantial portions of the
  * Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  *
  */

 #include "intel_drv.h"

 static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
 {
 	uint8_t 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_DEBUG_KMS("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_DEBUG_KMS("Failed to %s aux backlight\n",
 			      enable ? "enable" : "disable");
 	}
 }

 /*
  * 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 uint32_t intel_dp_aux_get_backlight(struct intel_connector *connector)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
 	uint8_t read_val[2] = { 0x0 };
 	uint16_t level = 0;

 	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
 			     &read_val, sizeof(read_val)) < 0) {
 		DRM_DEBUG_KMS("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;
 }

 /*
  * 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_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 = enc_to_intel_dp(&connector->encoder->base);
 	uint8_t vals[2] = { 0x0 };

 	vals[0] = level;

 	/* 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_DEBUG_KMS("Failed to write aux backlight level\n");
 		return;
 	}
 }

 /*
  * 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 = enc_to_intel_dp(&connector->encoder->base);
 	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
 	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 false;
 	}

 	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 false;
 	}
 	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 false;
 	}
 	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 false;
 	}

 	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 false;
 	}
 	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 false;
 	}
 	return true;
 }

 static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
 					  const struct drm_connector_state *conn_state)
 {
 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
 	uint8_t dpcd_buf, new_dpcd_buf, edp_backlight_mode;

 	if (drm_dp_dpcd_readb(&intel_dp->aux,
 			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
 		DRM_DEBUG_KMS("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;
 		break;

 	/* Do nothing when it is already DPCD mode */
 	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
 	default:
 		break;
 	}

 	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
 		if (intel_dp_aux_set_pwm_freq(connector))
 			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) {
 			DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
 		}
 	}

 	set_aux_backlight_enable(intel_dp, true);
 	intel_dp_aux_set_backlight(conn_state, connector->panel.backlight.level);
 }

 static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old_conn_state)
 {
 	set_aux_backlight_enable(enc_to_intel_dp(old_conn_state->best_encoder), false);
 }

 static int intel_dp_aux_setup_backlight(struct intel_connector *connector,
 					enum pipe pipe)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
 	struct intel_panel *panel = &connector->panel;

 	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
 		panel->backlight.max = 0xFFFF;
 	else
 		panel->backlight.max = 0xFF;

 	panel->backlight.min = 0;
 	panel->backlight.level = intel_dp_aux_get_backlight(connector);

 	panel->backlight.enabled = panel->backlight.level != 0;

 	return 0;
 }

 static bool
 intel_dp_aux_display_control_capable(struct intel_connector *connector)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);

 	/* Check the eDP Display control capabilities registers to determine if
 	 * the panel can support backlight control over the aux channel
 	 */
 	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
 	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
 	    !(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
 		DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
 		return true;
 	}
 	return false;
 }

 int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
 {
 	struct intel_panel *panel = &intel_connector->panel;

 	if (!i915_modparams.enable_dpcd_backlight)
 		return -ENODEV;

 	if (!intel_dp_aux_display_control_capable(intel_connector))
 		return -ENODEV;

 	panel->backlight.setup = intel_dp_aux_setup_backlight;
 	panel->backlight.enable = intel_dp_aux_enable_backlight;
 	panel->backlight.disable = intel_dp_aux_disable_backlight;
 	panel->backlight.set = intel_dp_aux_set_backlight;
 	panel->backlight.get = intel_dp_aux_get_backlight;

 	return 0;
 }
	/*
	* Copyright © 2015 Intel Corporation
	*
	* Permission is hereby granted, free of charge, to any person obtaining a
	* copy of this software and associated documentation files (the "Software"),
	* to deal in the Software without restriction, including without limitation
	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	* and/or sell copies of the Software, and to permit persons to whom the
	* Software is furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice (including the next
	* paragraph) shall be included in all copies or substantial portions of the
	* Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
	* IN THE SOFTWARE.
	*
	*/

	#include "intel_drv.h"

	static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
	{
	uint8_t 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_DEBUG_KMS("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_DEBUG_KMS("Failed to %s aux backlight\n",
	enable ? "enable" : "disable");
	}
	}

	/*
	* 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 uint32_t intel_dp_aux_get_backlight(struct intel_connector *connector)
	{
	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
	uint8_t read_val[2] = { 0x0 };
	uint16_t level = 0;

	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
	&read_val, sizeof(read_val)) < 0) {
	DRM_DEBUG_KMS("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;
	}

	/*
	* 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_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 = enc_to_intel_dp(&connector->encoder->base);
	uint8_t vals[2] = { 0x0 };

	vals[0] = level;

	/* 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_DEBUG_KMS("Failed to write aux backlight level\n");
	return;
	}
	}

	/*
	* 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 = enc_to_intel_dp(&connector->encoder->base);
	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
	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 false;
	}

	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 false;
	}
	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 false;
	}
	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 false;
	}

	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 false;
	}
	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 false;
	}
	return true;
	}

	static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
	const struct drm_connector_state *conn_state)
	{
	struct intel_connector *connector = to_intel_connector(conn_state->connector);
	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
	uint8_t dpcd_buf, new_dpcd_buf, edp_backlight_mode;

	if (drm_dp_dpcd_readb(&intel_dp->aux,
	DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
	DRM_DEBUG_KMS("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;
	break;

	/* Do nothing when it is already DPCD mode */
	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
	default:
	break;
	}

	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
	if (intel_dp_aux_set_pwm_freq(connector))
	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) {
	DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
	}
	}

	set_aux_backlight_enable(intel_dp, true);
	intel_dp_aux_set_backlight(conn_state, connector->panel.backlight.level);
	}

	static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old_conn_state)
	{
	set_aux_backlight_enable(enc_to_intel_dp(old_conn_state->best_encoder), false);
	}

	static int intel_dp_aux_setup_backlight(struct intel_connector *connector,
	enum pipe pipe)
	{
	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
	struct intel_panel *panel = &connector->panel;

	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
	panel->backlight.max = 0xFFFF;
	else
	panel->backlight.max = 0xFF;

	panel->backlight.min = 0;
	panel->backlight.level = intel_dp_aux_get_backlight(connector);

	panel->backlight.enabled = panel->backlight.level != 0;

	return 0;
	}

	static bool
	intel_dp_aux_display_control_capable(struct intel_connector *connector)
	{
	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);

	/* Check the eDP Display control capabilities registers to determine if
	* the panel can support backlight control over the aux channel
	*/
	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
	(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
	!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
	DRM_DEBUG_KMS("AUX Backlight Control Supported!\n");
	return true;
	}
	return false;
	}

	int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector)
	{
	struct intel_panel *panel = &intel_connector->panel;

	if (!i915_modparams.enable_dpcd_backlight)
	return -ENODEV;

	if (!intel_dp_aux_display_control_capable(intel_connector))
	return -ENODEV;

	panel->backlight.setup = intel_dp_aux_setup_backlight;
	panel->backlight.enable = intel_dp_aux_enable_backlight;
	panel->backlight.disable = intel_dp_aux_disable_backlight;
	panel->backlight.set = intel_dp_aux_set_backlight;
	panel->backlight.get = intel_dp_aux_get_backlight;

	return 0;
	}