1 /*
2  * Copyright © 2015 Intel Corporation
3  *
4  * Permission is hereby granted, free of charge, to any person obtaining a
5  * copy of this software and associated documentation files (the "Software"),
6  * to deal in the Software without restriction, including without limitation
7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8  * and/or sell copies of the Software, and to permit persons to whom the
9  * Software is furnished to do so, subject to the following conditions:
10  *
11  * The above copyright notice and this permission notice (including the next
12  * paragraph) shall be included in all copies or substantial portions of the
13  * Software.
14  *
15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21  * IN THE SOFTWARE.
22  *
23  */
24 
25 /*
26  * Laptops with Intel GPUs which have panels that support controlling the
27  * backlight through DP AUX can actually use two different interfaces: Intel's
28  * proprietary DP AUX backlight interface, and the standard VESA backlight
29  * interface. Unfortunately, at the time of writing this a lot of laptops will
30  * advertise support for the standard VESA backlight interface when they
31  * don't properly support it. However, on these systems the Intel backlight
32  * interface generally does work properly. Additionally, these systems will
33  * usually just indicate that they use PWM backlight controls in their VBIOS
34  * for some reason.
35  */
36 
37 #include "i915_drv.h"
38 #include "intel_backlight.h"
39 #include "intel_display_types.h"
40 #include "intel_dp.h"
41 #include "intel_dp_aux_backlight.h"
42 
43 /* TODO:
44  * Implement HDR, right now we just implement the bare minimum to bring us back into SDR mode so we
45  * can make people's backlights work in the mean time
46  */
47 
48 /*
49  * DP AUX registers for Intel's proprietary HDR backlight interface. We define
50  * them here since we'll likely be the only driver to ever use these.
51  */
52 #define INTEL_EDP_HDR_TCON_CAP0                                        0x340
53 
54 #define INTEL_EDP_HDR_TCON_CAP1                                        0x341
55 # define INTEL_EDP_HDR_TCON_2084_DECODE_CAP                           BIT(0)
56 # define INTEL_EDP_HDR_TCON_2020_GAMUT_CAP                            BIT(1)
57 # define INTEL_EDP_HDR_TCON_TONE_MAPPING_CAP                          BIT(2)
58 # define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_CAP                   BIT(3)
59 # define INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP                       BIT(4)
60 # define INTEL_EDP_HDR_TCON_OPTIMIZATION_CAP                          BIT(5)
61 # define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_CAP                       BIT(6)
62 # define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_CONVERSION_CAP        BIT(7)
63 
64 #define INTEL_EDP_HDR_TCON_CAP2                                        0x342
65 # define INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP                        BIT(0)
66 
67 #define INTEL_EDP_HDR_TCON_CAP3                                        0x343
68 
69 #define INTEL_EDP_HDR_GETSET_CTRL_PARAMS                               0x344
70 # define INTEL_EDP_HDR_TCON_2084_DECODE_ENABLE                        BIT(0)
71 # define INTEL_EDP_HDR_TCON_2020_GAMUT_ENABLE                         BIT(1)
72 # define INTEL_EDP_HDR_TCON_TONE_MAPPING_ENABLE                       BIT(2) /* Pre-TGL+ */
73 # define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_ENABLE                BIT(3)
74 # define INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE                     BIT(4)
75 # define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_ENABLE                BIT(5)
76 /* Bit 6 is reserved */
77 # define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_ENABLE                    BIT(7)
78 
79 #define INTEL_EDP_HDR_CONTENT_LUMINANCE                                0x346 /* Pre-TGL+ */
80 #define INTEL_EDP_HDR_PANEL_LUMINANCE_OVERRIDE                         0x34A
81 #define INTEL_EDP_SDR_LUMINANCE_LEVEL                                  0x352
82 #define INTEL_EDP_BRIGHTNESS_NITS_LSB                                  0x354
83 #define INTEL_EDP_BRIGHTNESS_NITS_MSB                                  0x355
84 #define INTEL_EDP_BRIGHTNESS_DELAY_FRAMES                              0x356
85 #define INTEL_EDP_BRIGHTNESS_PER_FRAME_STEPS                           0x357
86 
87 #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_0                            0x358
88 # define INTEL_EDP_TCON_USAGE_MASK                             GENMASK(0, 3)
89 # define INTEL_EDP_TCON_USAGE_UNKNOWN                                    0x0
90 # define INTEL_EDP_TCON_USAGE_DESKTOP                                    0x1
91 # define INTEL_EDP_TCON_USAGE_FULL_SCREEN_MEDIA                          0x2
92 # define INTEL_EDP_TCON_USAGE_FULL_SCREEN_GAMING                         0x3
93 # define INTEL_EDP_TCON_POWER_MASK                                    BIT(4)
94 # define INTEL_EDP_TCON_POWER_DC                                    (0 << 4)
95 # define INTEL_EDP_TCON_POWER_AC                                    (1 << 4)
96 # define INTEL_EDP_TCON_OPTIMIZATION_STRENGTH_MASK             GENMASK(5, 7)
97 
98 #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_1                            0x359
99 
100 enum intel_dp_aux_backlight_modparam {
101 	INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
102 	INTEL_DP_AUX_BACKLIGHT_OFF = 0,
103 	INTEL_DP_AUX_BACKLIGHT_ON = 1,
104 	INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
105 	INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
106 };
107 
108 /* Intel EDP backlight callbacks */
109 static bool
intel_dp_aux_supports_hdr_backlight(struct intel_connector * connector)110 intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
111 {
112 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
113 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
114 	struct drm_dp_aux *aux = &intel_dp->aux;
115 	struct intel_panel *panel = &connector->panel;
116 	int ret;
117 	u8 tcon_cap[4];
118 
119 	intel_dp_wait_source_oui(intel_dp);
120 
121 	ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0, tcon_cap, sizeof(tcon_cap));
122 	if (ret != sizeof(tcon_cap))
123 		return false;
124 
125 	if (!(tcon_cap[1] & INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP))
126 		return false;
127 
128 	if (tcon_cap[0] >= 1) {
129 		drm_dbg_kms(&i915->drm, "Detected Intel HDR backlight interface version %d\n",
130 			    tcon_cap[0]);
131 	} else {
132 		drm_dbg_kms(&i915->drm, "Detected unsupported HDR backlight interface version %d\n",
133 			    tcon_cap[0]);
134 		return false;
135 	}
136 
137 	/*
138 	 * If we don't have HDR static metadata there is no way to
139 	 * runtime detect used range for nits based control. For now
140 	 * do not use Intel proprietary eDP backlight control if we
141 	 * don't have this data in panel EDID. In case we find panel
142 	 * which supports only nits based control, but doesn't provide
143 	 * HDR static metadata we need to start maintaining table of
144 	 * ranges for such panels.
145 	 */
146 	if (i915->params.enable_dpcd_backlight != INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL &&
147 	    !(connector->base.hdr_sink_metadata.hdmi_type1.metadata_type &
148 	      BIT(HDMI_STATIC_METADATA_TYPE1))) {
149 		drm_info(&i915->drm,
150 			 "Panel is missing HDR static metadata. Possible support for Intel HDR backlight interface is not used. If your backlight controls don't work try booting with i915.enable_dpcd_backlight=%d. needs this, please file a _new_ bug report on drm/i915, see " FDO_BUG_URL " for details.\n",
151 			 INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL);
152 		return false;
153 	}
154 
155 	panel->backlight.edp.intel.sdr_uses_aux =
156 		tcon_cap[2] & INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP;
157 
158 	return true;
159 }
160 
161 static u32
intel_dp_aux_hdr_get_backlight(struct intel_connector * connector,enum pipe pipe)162 intel_dp_aux_hdr_get_backlight(struct intel_connector *connector, enum pipe pipe)
163 {
164 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
165 	struct intel_panel *panel = &connector->panel;
166 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
167 	u8 tmp;
168 	u8 buf[2] = { 0 };
169 
170 	if (drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &tmp) != 1) {
171 		drm_err(&i915->drm, "Failed to read current backlight mode from DPCD\n");
172 		return 0;
173 	}
174 
175 	if (!(tmp & INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE)) {
176 		if (!panel->backlight.edp.intel.sdr_uses_aux) {
177 			u32 pwm_level = panel->backlight.pwm_funcs->get(connector, pipe);
178 
179 			return intel_backlight_level_from_pwm(connector, pwm_level);
180 		}
181 
182 		/* Assume 100% brightness if backlight controls aren't enabled yet */
183 		return panel->backlight.max;
184 	}
185 
186 	if (drm_dp_dpcd_read(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
187 			     sizeof(buf)) != sizeof(buf)) {
188 		drm_err(&i915->drm, "Failed to read brightness from DPCD\n");
189 		return 0;
190 	}
191 
192 	return (buf[1] << 8 | buf[0]);
193 }
194 
195 static void
intel_dp_aux_hdr_set_aux_backlight(const struct drm_connector_state * conn_state,u32 level)196 intel_dp_aux_hdr_set_aux_backlight(const struct drm_connector_state *conn_state, u32 level)
197 {
198 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
199 	struct drm_device *dev = connector->base.dev;
200 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
201 	u8 buf[4] = { 0 };
202 
203 	buf[0] = level & 0xFF;
204 	buf[1] = (level & 0xFF00) >> 8;
205 
206 	if (drm_dp_dpcd_write(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
207 			      sizeof(buf)) != sizeof(buf))
208 		drm_err(dev, "Failed to write brightness level to DPCD\n");
209 }
210 
211 static void
intel_dp_aux_hdr_set_backlight(const struct drm_connector_state * conn_state,u32 level)212 intel_dp_aux_hdr_set_backlight(const struct drm_connector_state *conn_state, u32 level)
213 {
214 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
215 	struct intel_panel *panel = &connector->panel;
216 
217 	if (panel->backlight.edp.intel.sdr_uses_aux) {
218 		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
219 	} else {
220 		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
221 
222 		intel_backlight_set_pwm_level(conn_state, pwm_level);
223 	}
224 }
225 
226 static void
intel_dp_aux_hdr_enable_backlight(const struct intel_crtc_state * crtc_state,const struct drm_connector_state * conn_state,u32 level)227 intel_dp_aux_hdr_enable_backlight(const struct intel_crtc_state *crtc_state,
228 				  const struct drm_connector_state *conn_state, u32 level)
229 {
230 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
231 	struct intel_panel *panel = &connector->panel;
232 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
233 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
234 	int ret;
235 	u8 old_ctrl, ctrl;
236 
237 	intel_dp_wait_source_oui(intel_dp);
238 
239 	ret = drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &old_ctrl);
240 	if (ret != 1) {
241 		drm_err(&i915->drm, "Failed to read current backlight control mode: %d\n", ret);
242 		return;
243 	}
244 
245 	ctrl = old_ctrl;
246 	if (panel->backlight.edp.intel.sdr_uses_aux) {
247 		ctrl |= INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
248 		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
249 	} else {
250 		u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
251 
252 		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
253 
254 		ctrl &= ~INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
255 	}
256 
257 	if (ctrl != old_ctrl)
258 		if (drm_dp_dpcd_writeb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, ctrl) != 1)
259 			drm_err(&i915->drm, "Failed to configure DPCD brightness controls\n");
260 }
261 
262 static void
intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state * conn_state,u32 level)263 intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state *conn_state, u32 level)
264 {
265 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
266 	struct intel_panel *panel = &connector->panel;
267 
268 	/* Nothing to do for AUX based backlight controls */
269 	if (panel->backlight.edp.intel.sdr_uses_aux)
270 		return;
271 
272 	/* Note we want the actual pwm_level to be 0, regardless of pwm_min */
273 	panel->backlight.pwm_funcs->disable(conn_state, intel_backlight_invert_pwm_level(connector, 0));
274 }
275 
276 static int
intel_dp_aux_hdr_setup_backlight(struct intel_connector * connector,enum pipe pipe)277 intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pipe)
278 {
279 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
280 	struct intel_panel *panel = &connector->panel;
281 	int ret;
282 
283 	if (panel->backlight.edp.intel.sdr_uses_aux) {
284 		drm_dbg_kms(&i915->drm, "SDR backlight is controlled through DPCD\n");
285 	} else {
286 		drm_dbg_kms(&i915->drm, "SDR backlight is controlled through PWM\n");
287 
288 		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
289 		if (ret < 0) {
290 			drm_err(&i915->drm,
291 				"Failed to setup SDR backlight controls through PWM: %d\n", ret);
292 			return ret;
293 		}
294 	}
295 
296 	panel->backlight.max = 512;
297 	panel->backlight.min = 0;
298 	panel->backlight.level = intel_dp_aux_hdr_get_backlight(connector, pipe);
299 	panel->backlight.enabled = panel->backlight.level != 0;
300 
301 	return 0;
302 }
303 
304 /* VESA backlight callbacks */
intel_dp_aux_vesa_get_backlight(struct intel_connector * connector,enum pipe unused)305 static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
306 {
307 	return connector->panel.backlight.level;
308 }
309 
310 static void
intel_dp_aux_vesa_set_backlight(const struct drm_connector_state * conn_state,u32 level)311 intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
312 {
313 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
314 	struct intel_panel *panel = &connector->panel;
315 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
316 
317 	if (!panel->backlight.edp.vesa.info.aux_set) {
318 		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
319 
320 		intel_backlight_set_pwm_level(conn_state, pwm_level);
321 	}
322 
323 	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
324 }
325 
326 static void
intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state * crtc_state,const struct drm_connector_state * conn_state,u32 level)327 intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
328 				   const struct drm_connector_state *conn_state, u32 level)
329 {
330 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
331 	struct intel_panel *panel = &connector->panel;
332 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
333 
334 	if (!panel->backlight.edp.vesa.info.aux_enable) {
335 		u32 pwm_level;
336 
337 		if (!panel->backlight.edp.vesa.info.aux_set)
338 			pwm_level = intel_backlight_level_to_pwm(connector, level);
339 		else
340 			pwm_level = intel_backlight_invert_pwm_level(connector,
341 								     panel->backlight.pwm_level_max);
342 
343 		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
344 	}
345 
346 	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
347 }
348 
intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state * old_conn_state,u32 level)349 static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
350 						u32 level)
351 {
352 	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
353 	struct intel_panel *panel = &connector->panel;
354 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
355 
356 	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
357 
358 	if (!panel->backlight.edp.vesa.info.aux_enable)
359 		panel->backlight.pwm_funcs->disable(old_conn_state,
360 						    intel_backlight_invert_pwm_level(connector, 0));
361 }
362 
intel_dp_aux_vesa_setup_backlight(struct intel_connector * connector,enum pipe pipe)363 static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
364 {
365 	struct intel_dp *intel_dp = intel_attached_dp(connector);
366 	struct intel_panel *panel = &connector->panel;
367 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
368 	u16 current_level;
369 	u8 current_mode;
370 	int ret;
371 
372 	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
373 				     i915->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
374 				     &current_level, &current_mode);
375 	if (ret < 0)
376 		return ret;
377 
378 	if (!panel->backlight.edp.vesa.info.aux_set || !panel->backlight.edp.vesa.info.aux_enable) {
379 		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
380 		if (ret < 0) {
381 			drm_err(&i915->drm,
382 				"Failed to setup PWM backlight controls for eDP backlight: %d\n",
383 				ret);
384 			return ret;
385 		}
386 	}
387 
388 	if (panel->backlight.edp.vesa.info.aux_set) {
389 		panel->backlight.max = panel->backlight.edp.vesa.info.max;
390 		panel->backlight.min = 0;
391 		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
392 			panel->backlight.level = current_level;
393 			panel->backlight.enabled = panel->backlight.level != 0;
394 		} else {
395 			panel->backlight.level = panel->backlight.max;
396 			panel->backlight.enabled = false;
397 		}
398 	} else {
399 		panel->backlight.max = panel->backlight.pwm_level_max;
400 		panel->backlight.min = panel->backlight.pwm_level_min;
401 		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_PWM) {
402 			panel->backlight.level = panel->backlight.pwm_funcs->get(connector, pipe);
403 			panel->backlight.enabled = panel->backlight.pwm_enabled;
404 		} else {
405 			panel->backlight.level = panel->backlight.max;
406 			panel->backlight.enabled = false;
407 		}
408 	}
409 
410 	return 0;
411 }
412 
413 static bool
intel_dp_aux_supports_vesa_backlight(struct intel_connector * connector)414 intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
415 {
416 	struct intel_dp *intel_dp = intel_attached_dp(connector);
417 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
418 
419 	if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
420 		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
421 		return true;
422 	}
423 	return false;
424 }
425 
426 static const struct intel_panel_bl_funcs intel_dp_hdr_bl_funcs = {
427 	.setup = intel_dp_aux_hdr_setup_backlight,
428 	.enable = intel_dp_aux_hdr_enable_backlight,
429 	.disable = intel_dp_aux_hdr_disable_backlight,
430 	.set = intel_dp_aux_hdr_set_backlight,
431 	.get = intel_dp_aux_hdr_get_backlight,
432 };
433 
434 static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
435 	.setup = intel_dp_aux_vesa_setup_backlight,
436 	.enable = intel_dp_aux_vesa_enable_backlight,
437 	.disable = intel_dp_aux_vesa_disable_backlight,
438 	.set = intel_dp_aux_vesa_set_backlight,
439 	.get = intel_dp_aux_vesa_get_backlight,
440 };
441 
intel_dp_aux_init_backlight_funcs(struct intel_connector * connector)442 int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
443 {
444 	struct drm_device *dev = connector->base.dev;
445 	struct intel_panel *panel = &connector->panel;
446 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
447 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
448 	bool try_intel_interface = false, try_vesa_interface = false;
449 
450 	/* Check the VBT and user's module parameters to figure out which
451 	 * interfaces to probe
452 	 */
453 	switch (i915->params.enable_dpcd_backlight) {
454 	case INTEL_DP_AUX_BACKLIGHT_OFF:
455 		return -ENODEV;
456 	case INTEL_DP_AUX_BACKLIGHT_AUTO:
457 		switch (i915->vbt.backlight.type) {
458 		case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
459 			try_vesa_interface = true;
460 			break;
461 		case INTEL_BACKLIGHT_DISPLAY_DDI:
462 			try_intel_interface = true;
463 			break;
464 		default:
465 			return -ENODEV;
466 		}
467 		break;
468 	case INTEL_DP_AUX_BACKLIGHT_ON:
469 		if (i915->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
470 			try_intel_interface = true;
471 
472 		try_vesa_interface = true;
473 		break;
474 	case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
475 		try_vesa_interface = true;
476 		break;
477 	case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
478 		try_intel_interface = true;
479 		break;
480 	}
481 
482 	/*
483 	 * Since Intel has their own backlight control interface, the majority of machines out there
484 	 * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to
485 	 * the VESA interface. However, other GPUs (such as Nvidia's) will always use the VESA
486 	 * interface. This means that there's quite a number of panels out there that will advertise
487 	 * support for both interfaces, primarily systems with Intel/Nvidia hybrid GPU setups.
488 	 *
489 	 * There's a catch to this though: on many panels that advertise support for both
490 	 * interfaces, the VESA backlight interface will stop working once we've programmed the
491 	 * panel with Intel's OUI - which is also required for us to be able to detect Intel's
492 	 * backlight interface at all. This means that the only sensible way for us to detect both
493 	 * interfaces is to probe for Intel's first, and VESA's second.
494 	 */
495 	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
496 		drm_dbg_kms(dev, "Using Intel proprietary eDP backlight controls\n");
497 		panel->backlight.funcs = &intel_dp_hdr_bl_funcs;
498 		return 0;
499 	}
500 
501 	if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
502 		drm_dbg_kms(dev, "Using VESA eDP backlight controls\n");
503 		panel->backlight.funcs = &intel_dp_vesa_bl_funcs;
504 		return 0;
505 	}
506 
507 	return -ENODEV;
508 }
509