xref: /openbsd-src/sys/dev/pci/drm/i915/display/intel_dp_aux_backlight.c (revision 8550894424f8a4aa4aafb6cd57229dd6ed7cd9dd)
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 <linux/kconfig.h>
38 #include "i915_drv.h"
39 #include "intel_backlight.h"
40 #include "intel_display_types.h"
41 #include "intel_dp.h"
42 #include "intel_dp_aux_backlight.h"
43 
44 /* TODO:
45  * Implement HDR, right now we just implement the bare minimum to bring us back into SDR mode so we
46  * can make people's backlights work in the mean time
47  */
48 
49 /*
50  * DP AUX registers for Intel's proprietary HDR backlight interface. We define
51  * them here since we'll likely be the only driver to ever use these.
52  */
53 #define INTEL_EDP_HDR_TCON_CAP0                                        0x340
54 
55 #define INTEL_EDP_HDR_TCON_CAP1                                        0x341
56 # define INTEL_EDP_HDR_TCON_2084_DECODE_CAP                           BIT(0)
57 # define INTEL_EDP_HDR_TCON_2020_GAMUT_CAP                            BIT(1)
58 # define INTEL_EDP_HDR_TCON_TONE_MAPPING_CAP                          BIT(2)
59 # define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_CAP                   BIT(3)
60 # define INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP                       BIT(4)
61 # define INTEL_EDP_HDR_TCON_OPTIMIZATION_CAP                          BIT(5)
62 # define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_CAP                       BIT(6)
63 # define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_CONVERSION_CAP        BIT(7)
64 
65 #define INTEL_EDP_HDR_TCON_CAP2                                        0x342
66 # define INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP                        BIT(0)
67 
68 #define INTEL_EDP_HDR_TCON_CAP3                                        0x343
69 
70 #define INTEL_EDP_HDR_GETSET_CTRL_PARAMS                               0x344
71 # define INTEL_EDP_HDR_TCON_2084_DECODE_ENABLE                        BIT(0)
72 # define INTEL_EDP_HDR_TCON_2020_GAMUT_ENABLE                         BIT(1)
73 # define INTEL_EDP_HDR_TCON_TONE_MAPPING_ENABLE                       BIT(2) /* Pre-TGL+ */
74 # define INTEL_EDP_HDR_TCON_SEGMENTED_BACKLIGHT_ENABLE                BIT(3)
75 # define INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE                     BIT(4)
76 # define INTEL_EDP_HDR_TCON_SRGB_TO_PANEL_GAMUT_ENABLE                BIT(5)
77 /* Bit 6 is reserved */
78 # define INTEL_EDP_HDR_TCON_SDP_COLORIMETRY_ENABLE                    BIT(7)
79 
80 #define INTEL_EDP_HDR_CONTENT_LUMINANCE                                0x346 /* Pre-TGL+ */
81 #define INTEL_EDP_HDR_PANEL_LUMINANCE_OVERRIDE                         0x34A
82 #define INTEL_EDP_SDR_LUMINANCE_LEVEL                                  0x352
83 #define INTEL_EDP_BRIGHTNESS_NITS_LSB                                  0x354
84 #define INTEL_EDP_BRIGHTNESS_NITS_MSB                                  0x355
85 #define INTEL_EDP_BRIGHTNESS_DELAY_FRAMES                              0x356
86 #define INTEL_EDP_BRIGHTNESS_PER_FRAME_STEPS                           0x357
87 
88 #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_0                            0x358
89 # define INTEL_EDP_TCON_USAGE_MASK                             GENMASK(0, 3)
90 # define INTEL_EDP_TCON_USAGE_UNKNOWN                                    0x0
91 # define INTEL_EDP_TCON_USAGE_DESKTOP                                    0x1
92 # define INTEL_EDP_TCON_USAGE_FULL_SCREEN_MEDIA                          0x2
93 # define INTEL_EDP_TCON_USAGE_FULL_SCREEN_GAMING                         0x3
94 # define INTEL_EDP_TCON_POWER_MASK                                    BIT(4)
95 # define INTEL_EDP_TCON_POWER_DC                                    (0 << 4)
96 # define INTEL_EDP_TCON_POWER_AC                                    (1 << 4)
97 # define INTEL_EDP_TCON_OPTIMIZATION_STRENGTH_MASK             GENMASK(5, 7)
98 
99 #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_1                            0x359
100 
101 enum intel_dp_aux_backlight_modparam {
102 	INTEL_DP_AUX_BACKLIGHT_AUTO = -1,
103 	INTEL_DP_AUX_BACKLIGHT_OFF = 0,
104 	INTEL_DP_AUX_BACKLIGHT_ON = 1,
105 	INTEL_DP_AUX_BACKLIGHT_FORCE_VESA = 2,
106 	INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL = 3,
107 };
108 
109 /* Intel EDP backlight callbacks */
110 static bool
111 intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
112 {
113 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
114 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
115 	struct drm_dp_aux *aux = &intel_dp->aux;
116 	struct intel_panel *panel = &connector->panel;
117 	int ret;
118 	u8 tcon_cap[4];
119 
120 	intel_dp_wait_source_oui(intel_dp);
121 
122 	ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0, tcon_cap, sizeof(tcon_cap));
123 	if (ret != sizeof(tcon_cap))
124 		return false;
125 
126 	if (!(tcon_cap[1] & INTEL_EDP_HDR_TCON_BRIGHTNESS_NITS_CAP))
127 		return false;
128 
129 	if (tcon_cap[0] >= 1) {
130 		drm_dbg_kms(&i915->drm, "Detected Intel HDR backlight interface version %d\n",
131 			    tcon_cap[0]);
132 	} else {
133 		drm_dbg_kms(&i915->drm, "Detected unsupported HDR backlight interface version %d\n",
134 			    tcon_cap[0]);
135 		return false;
136 	}
137 
138 	/*
139 	 * If we don't have HDR static metadata there is no way to
140 	 * runtime detect used range for nits based control. For now
141 	 * do not use Intel proprietary eDP backlight control if we
142 	 * don't have this data in panel EDID. In case we find panel
143 	 * which supports only nits based control, but doesn't provide
144 	 * HDR static metadata we need to start maintaining table of
145 	 * ranges for such panels.
146 	 */
147 	if (i915->params.enable_dpcd_backlight != INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL &&
148 	    !(connector->base.hdr_sink_metadata.hdmi_type1.metadata_type &
149 	      BIT(HDMI_STATIC_METADATA_TYPE1))) {
150 		drm_info(&i915->drm,
151 			 "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",
152 			 INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL);
153 		return false;
154 	}
155 
156 	panel->backlight.edp.intel.sdr_uses_aux =
157 		tcon_cap[2] & INTEL_EDP_SDR_TCON_BRIGHTNESS_AUX_CAP;
158 
159 	return true;
160 }
161 
162 static u32
163 intel_dp_aux_hdr_get_backlight(struct intel_connector *connector, enum pipe pipe)
164 {
165 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
166 	struct intel_panel *panel = &connector->panel;
167 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
168 	u8 tmp;
169 	u8 buf[2] = { 0 };
170 
171 	if (drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &tmp) != 1) {
172 		drm_err(&i915->drm, "Failed to read current backlight mode from DPCD\n");
173 		return 0;
174 	}
175 
176 	if (!(tmp & INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE)) {
177 		if (!panel->backlight.edp.intel.sdr_uses_aux) {
178 			u32 pwm_level = panel->backlight.pwm_funcs->get(connector, pipe);
179 
180 			return intel_backlight_level_from_pwm(connector, pwm_level);
181 		}
182 
183 		/* Assume 100% brightness if backlight controls aren't enabled yet */
184 		return panel->backlight.max;
185 	}
186 
187 	if (drm_dp_dpcd_read(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
188 			     sizeof(buf)) != sizeof(buf)) {
189 		drm_err(&i915->drm, "Failed to read brightness from DPCD\n");
190 		return 0;
191 	}
192 
193 	return (buf[1] << 8 | buf[0]);
194 }
195 
196 static void
197 intel_dp_aux_hdr_set_aux_backlight(const struct drm_connector_state *conn_state, u32 level)
198 {
199 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
200 	struct drm_device *dev = connector->base.dev;
201 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
202 	u8 buf[4] = { 0 };
203 
204 	buf[0] = level & 0xFF;
205 	buf[1] = (level & 0xFF00) >> 8;
206 
207 	if (drm_dp_dpcd_write(&intel_dp->aux, INTEL_EDP_BRIGHTNESS_NITS_LSB, buf,
208 			      sizeof(buf)) != sizeof(buf))
209 		drm_err(dev, "Failed to write brightness level to DPCD\n");
210 }
211 
212 static void
213 intel_dp_aux_hdr_set_backlight(const struct drm_connector_state *conn_state, u32 level)
214 {
215 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
216 	struct intel_panel *panel = &connector->panel;
217 
218 	if (panel->backlight.edp.intel.sdr_uses_aux) {
219 		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
220 	} else {
221 		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
222 
223 		intel_backlight_set_pwm_level(conn_state, pwm_level);
224 	}
225 }
226 
227 static void
228 intel_dp_aux_hdr_enable_backlight(const struct intel_crtc_state *crtc_state,
229 				  const struct drm_connector_state *conn_state, u32 level)
230 {
231 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
232 	struct intel_panel *panel = &connector->panel;
233 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
234 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
235 	int ret;
236 	u8 old_ctrl, ctrl;
237 
238 	intel_dp_wait_source_oui(intel_dp);
239 
240 	ret = drm_dp_dpcd_readb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &old_ctrl);
241 	if (ret != 1) {
242 		drm_err(&i915->drm, "Failed to read current backlight control mode: %d\n", ret);
243 		return;
244 	}
245 
246 	ctrl = old_ctrl;
247 	if (panel->backlight.edp.intel.sdr_uses_aux) {
248 		ctrl |= INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
249 		intel_dp_aux_hdr_set_aux_backlight(conn_state, level);
250 	} else {
251 		u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
252 
253 		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
254 
255 		ctrl &= ~INTEL_EDP_HDR_TCON_BRIGHTNESS_AUX_ENABLE;
256 	}
257 
258 	if (ctrl != old_ctrl)
259 		if (drm_dp_dpcd_writeb(&intel_dp->aux, INTEL_EDP_HDR_GETSET_CTRL_PARAMS, ctrl) != 1)
260 			drm_err(&i915->drm, "Failed to configure DPCD brightness controls\n");
261 }
262 
263 static void
264 intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state *conn_state, u32 level)
265 {
266 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
267 	struct intel_panel *panel = &connector->panel;
268 
269 	/* Nothing to do for AUX based backlight controls */
270 	if (panel->backlight.edp.intel.sdr_uses_aux)
271 		return;
272 
273 	/* Note we want the actual pwm_level to be 0, regardless of pwm_min */
274 	panel->backlight.pwm_funcs->disable(conn_state, intel_backlight_invert_pwm_level(connector, 0));
275 }
276 
277 static int
278 intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pipe)
279 {
280 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
281 	struct intel_panel *panel = &connector->panel;
282 	struct drm_luminance_range_info *luminance_range =
283 		&connector->base.display_info.luminance_range;
284 	int ret;
285 
286 	if (panel->backlight.edp.intel.sdr_uses_aux) {
287 		drm_dbg_kms(&i915->drm, "SDR backlight is controlled through DPCD\n");
288 	} else {
289 		drm_dbg_kms(&i915->drm, "SDR backlight is controlled through PWM\n");
290 
291 		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
292 		if (ret < 0) {
293 			drm_err(&i915->drm,
294 				"Failed to setup SDR backlight controls through PWM: %d\n", ret);
295 			return ret;
296 		}
297 	}
298 
299 	if (luminance_range->max_luminance) {
300 		panel->backlight.max = luminance_range->max_luminance;
301 		panel->backlight.min = luminance_range->min_luminance;
302 	} else {
303 		panel->backlight.max = 512;
304 		panel->backlight.min = 0;
305 	}
306 
307 	drm_dbg_kms(&i915->drm, "Using backlight range %d..%d\n", panel->backlight.min,
308 		    panel->backlight.max);
309 
310 	panel->backlight.level = intel_dp_aux_hdr_get_backlight(connector, pipe);
311 	panel->backlight.enabled = panel->backlight.level != 0;
312 
313 	return 0;
314 }
315 
316 /* VESA backlight callbacks */
317 static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
318 {
319 	return connector->panel.backlight.level;
320 }
321 
322 static void
323 intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
324 {
325 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
326 	struct intel_panel *panel = &connector->panel;
327 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
328 
329 	if (!panel->backlight.edp.vesa.info.aux_set) {
330 		const u32 pwm_level = intel_backlight_level_to_pwm(connector, level);
331 
332 		intel_backlight_set_pwm_level(conn_state, pwm_level);
333 	}
334 
335 	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
336 }
337 
338 static void
339 intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
340 				   const struct drm_connector_state *conn_state, u32 level)
341 {
342 	struct intel_connector *connector = to_intel_connector(conn_state->connector);
343 	struct intel_panel *panel = &connector->panel;
344 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
345 
346 	if (!panel->backlight.edp.vesa.info.aux_enable) {
347 		u32 pwm_level;
348 
349 		if (!panel->backlight.edp.vesa.info.aux_set)
350 			pwm_level = intel_backlight_level_to_pwm(connector, level);
351 		else
352 			pwm_level = intel_backlight_invert_pwm_level(connector,
353 								     panel->backlight.pwm_level_max);
354 
355 		panel->backlight.pwm_funcs->enable(crtc_state, conn_state, pwm_level);
356 	}
357 
358 	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
359 }
360 
361 static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
362 						u32 level)
363 {
364 	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
365 	struct intel_panel *panel = &connector->panel;
366 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
367 
368 	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
369 
370 	if (!panel->backlight.edp.vesa.info.aux_enable)
371 		panel->backlight.pwm_funcs->disable(old_conn_state,
372 						    intel_backlight_invert_pwm_level(connector, 0));
373 }
374 
375 static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
376 {
377 	struct intel_dp *intel_dp = intel_attached_dp(connector);
378 	struct intel_panel *panel = &connector->panel;
379 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
380 	u16 current_level;
381 	u8 current_mode;
382 	int ret;
383 
384 	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
385 				     panel->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
386 				     &current_level, &current_mode);
387 	if (ret < 0)
388 		return ret;
389 
390 	if (!panel->backlight.edp.vesa.info.aux_set || !panel->backlight.edp.vesa.info.aux_enable) {
391 		ret = panel->backlight.pwm_funcs->setup(connector, pipe);
392 		if (ret < 0) {
393 			drm_err(&i915->drm,
394 				"Failed to setup PWM backlight controls for eDP backlight: %d\n",
395 				ret);
396 			return ret;
397 		}
398 	}
399 
400 	if (panel->backlight.edp.vesa.info.aux_set) {
401 		panel->backlight.max = panel->backlight.edp.vesa.info.max;
402 		panel->backlight.min = 0;
403 		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
404 			panel->backlight.level = current_level;
405 			panel->backlight.enabled = panel->backlight.level != 0;
406 		} else {
407 			panel->backlight.level = panel->backlight.max;
408 			panel->backlight.enabled = false;
409 		}
410 	} else {
411 		panel->backlight.max = panel->backlight.pwm_level_max;
412 		panel->backlight.min = panel->backlight.pwm_level_min;
413 		if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_PWM) {
414 			panel->backlight.level = panel->backlight.pwm_funcs->get(connector, pipe);
415 			panel->backlight.enabled = panel->backlight.pwm_enabled;
416 		} else {
417 			panel->backlight.level = panel->backlight.max;
418 			panel->backlight.enabled = false;
419 		}
420 	}
421 
422 	return 0;
423 }
424 
425 static bool
426 intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
427 {
428 	struct intel_dp *intel_dp = intel_attached_dp(connector);
429 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
430 
431 	if (drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
432 		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
433 		return true;
434 	}
435 	return false;
436 }
437 
438 static const struct intel_panel_bl_funcs intel_dp_hdr_bl_funcs = {
439 	.setup = intel_dp_aux_hdr_setup_backlight,
440 	.enable = intel_dp_aux_hdr_enable_backlight,
441 	.disable = intel_dp_aux_hdr_disable_backlight,
442 	.set = intel_dp_aux_hdr_set_backlight,
443 	.get = intel_dp_aux_hdr_get_backlight,
444 };
445 
446 static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
447 	.setup = intel_dp_aux_vesa_setup_backlight,
448 	.enable = intel_dp_aux_vesa_enable_backlight,
449 	.disable = intel_dp_aux_vesa_disable_backlight,
450 	.set = intel_dp_aux_vesa_set_backlight,
451 	.get = intel_dp_aux_vesa_get_backlight,
452 };
453 
454 int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
455 {
456 	struct drm_device *dev = connector->base.dev;
457 	struct intel_panel *panel = &connector->panel;
458 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
459 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
460 	bool try_intel_interface = false, try_vesa_interface = false;
461 
462 	/* Check the VBT and user's module parameters to figure out which
463 	 * interfaces to probe
464 	 */
465 	switch (i915->params.enable_dpcd_backlight) {
466 	case INTEL_DP_AUX_BACKLIGHT_OFF:
467 		return -ENODEV;
468 	case INTEL_DP_AUX_BACKLIGHT_AUTO:
469 		switch (panel->vbt.backlight.type) {
470 		case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
471 			try_vesa_interface = true;
472 			break;
473 		case INTEL_BACKLIGHT_DISPLAY_DDI:
474 			try_intel_interface = true;
475 			break;
476 		default:
477 			return -ENODEV;
478 		}
479 		break;
480 	case INTEL_DP_AUX_BACKLIGHT_ON:
481 		if (panel->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
482 			try_intel_interface = true;
483 
484 		try_vesa_interface = true;
485 		break;
486 	case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
487 		try_vesa_interface = true;
488 		break;
489 	case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
490 		try_intel_interface = true;
491 		break;
492 	}
493 
494 	/*
495 	 * Since Intel has their own backlight control interface, the majority of machines out there
496 	 * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to
497 	 * the VESA interface. However, other GPUs (such as Nvidia's) will always use the VESA
498 	 * interface. This means that there's quite a number of panels out there that will advertise
499 	 * support for both interfaces, primarily systems with Intel/Nvidia hybrid GPU setups.
500 	 *
501 	 * There's a catch to this though: on many panels that advertise support for both
502 	 * interfaces, the VESA backlight interface will stop working once we've programmed the
503 	 * panel with Intel's OUI - which is also required for us to be able to detect Intel's
504 	 * backlight interface at all. This means that the only sensible way for us to detect both
505 	 * interfaces is to probe for Intel's first, and VESA's second.
506 	 */
507 	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
508 		drm_dbg_kms(dev, "Using Intel proprietary eDP backlight controls\n");
509 		panel->backlight.funcs = &intel_dp_hdr_bl_funcs;
510 		return 0;
511 	}
512 
513 	if (try_vesa_interface && intel_dp_aux_supports_vesa_backlight(connector)) {
514 		drm_dbg_kms(dev, "Using VESA eDP backlight controls\n");
515 		panel->backlight.funcs = &intel_dp_vesa_bl_funcs;
516 		return 0;
517 	}
518 
519 	return -ENODEV;
520 }
521