1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright 2021 Google Inc.
4  *
5  * The DP AUX bus is used for devices that are connected over a DisplayPort
6  * AUX bus. The device on the far side of the bus is referred to as an
7  * endpoint in this code.
8  *
9  * There is only one device connected to the DP AUX bus: an eDP panel.
10  * Though historically panels (even DP panels) have been modeled as simple
11  * platform devices, putting them under the DP AUX bus allows the panel driver
12  * to perform transactions on that bus.
13  */
14 
15 #include <linux/init.h>
16 #include <linux/kernel.h>
17 #include <linux/module.h>
18 #include <linux/of_device.h>
19 #include <linux/pm_domain.h>
20 #include <linux/pm_runtime.h>
21 
22 #include <drm/display/drm_dp_aux_bus.h>
23 #include <drm/display/drm_dp_helper.h>
24 
25 struct dp_aux_ep_device_with_data {
26 	struct dp_aux_ep_device aux_ep;
27 	int (*done_probing)(struct drm_dp_aux *aux);
28 };
29 
30 /**
31  * dp_aux_ep_match() - The match function for the dp_aux_bus.
32  * @dev: The device to match.
33  * @drv: The driver to try to match against.
34  *
35  * At the moment, we just match on device tree.
36  *
37  * Return: True if this driver matches this device; false otherwise.
38  */
39 static int dp_aux_ep_match(struct device *dev, struct device_driver *drv)
40 {
41 	return !!of_match_device(drv->of_match_table, dev);
42 }
43 
44 /**
45  * dp_aux_ep_probe() - The probe function for the dp_aux_bus.
46  * @dev: The device to probe.
47  *
48  * Calls through to the endpoint driver probe.
49  *
50  * Return: 0 if no error or negative error code.
51  */
52 static int dp_aux_ep_probe(struct device *dev)
53 {
54 	struct dp_aux_ep_driver *aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
55 	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);
56 	struct dp_aux_ep_device_with_data *aux_ep_with_data =
57 		container_of(aux_ep, struct dp_aux_ep_device_with_data, aux_ep);
58 	int ret;
59 
60 	ret = dev_pm_domain_attach(dev, true);
61 	if (ret)
62 		return dev_err_probe(dev, ret, "Failed to attach to PM Domain\n");
63 
64 	ret = aux_ep_drv->probe(aux_ep);
65 	if (ret)
66 		goto err_attached;
67 
68 	if (aux_ep_with_data->done_probing) {
69 		ret = aux_ep_with_data->done_probing(aux_ep->aux);
70 		if (ret) {
71 			/*
72 			 * The done_probing() callback should not return
73 			 * -EPROBE_DEFER to us. If it does, we treat it as an
74 			 * error. Passing it on as-is would cause the _panel_
75 			 * to defer.
76 			 */
77 			if (ret == -EPROBE_DEFER) {
78 				dev_err(dev,
79 					"DP AUX done_probing() can't defer\n");
80 				ret = -EINVAL;
81 			}
82 			goto err_probed;
83 		}
84 	}
85 
86 	return 0;
87 err_probed:
88 	if (aux_ep_drv->remove)
89 		aux_ep_drv->remove(aux_ep);
90 err_attached:
91 	dev_pm_domain_detach(dev, true);
92 
93 	return ret;
94 }
95 
96 /**
97  * dp_aux_ep_remove() - The remove function for the dp_aux_bus.
98  * @dev: The device to remove.
99  *
100  * Calls through to the endpoint driver remove.
101  */
102 static void dp_aux_ep_remove(struct device *dev)
103 {
104 	struct dp_aux_ep_driver *aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
105 	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);
106 
107 	if (aux_ep_drv->remove)
108 		aux_ep_drv->remove(aux_ep);
109 	dev_pm_domain_detach(dev, true);
110 }
111 
112 /**
113  * dp_aux_ep_shutdown() - The shutdown function for the dp_aux_bus.
114  * @dev: The device to shutdown.
115  *
116  * Calls through to the endpoint driver shutdown.
117  */
118 static void dp_aux_ep_shutdown(struct device *dev)
119 {
120 	struct dp_aux_ep_driver *aux_ep_drv;
121 
122 	if (!dev->driver)
123 		return;
124 
125 	aux_ep_drv = to_dp_aux_ep_drv(dev->driver);
126 	if (aux_ep_drv->shutdown)
127 		aux_ep_drv->shutdown(to_dp_aux_ep_dev(dev));
128 }
129 
130 static struct bus_type dp_aux_bus_type = {
131 	.name		= "dp-aux",
132 	.match		= dp_aux_ep_match,
133 	.probe		= dp_aux_ep_probe,
134 	.remove		= dp_aux_ep_remove,
135 	.shutdown	= dp_aux_ep_shutdown,
136 };
137 
138 static ssize_t modalias_show(struct device *dev,
139 			     struct device_attribute *attr, char *buf)
140 {
141 	return of_device_modalias(dev, buf, PAGE_SIZE);
142 }
143 static DEVICE_ATTR_RO(modalias);
144 
145 static struct attribute *dp_aux_ep_dev_attrs[] = {
146 	&dev_attr_modalias.attr,
147 	NULL,
148 };
149 ATTRIBUTE_GROUPS(dp_aux_ep_dev);
150 
151 /**
152  * dp_aux_ep_dev_release() - Free memory for the dp_aux_ep device
153  * @dev: The device to free.
154  */
155 static void dp_aux_ep_dev_release(struct device *dev)
156 {
157 	struct dp_aux_ep_device *aux_ep = to_dp_aux_ep_dev(dev);
158 	struct dp_aux_ep_device_with_data *aux_ep_with_data =
159 		container_of(aux_ep, struct dp_aux_ep_device_with_data, aux_ep);
160 
161 	kfree(aux_ep_with_data);
162 }
163 
164 static struct device_type dp_aux_device_type_type = {
165 	.groups		= dp_aux_ep_dev_groups,
166 	.uevent		= of_device_uevent_modalias,
167 	.release	= dp_aux_ep_dev_release,
168 };
169 
170 /**
171  * of_dp_aux_ep_destroy() - Destroy an DP AUX endpoint device
172  * @dev: The device to destroy.
173  * @data: Not used
174  *
175  * This is just used as a callback by of_dp_aux_depopulate_bus() and
176  * is called for _all_ of the child devices of the device providing the AUX bus.
177  * We'll only act on those that are of type "dp_aux_bus_type".
178  *
179  * This function is effectively an inverse of what's in
180  * of_dp_aux_populate_bus(). NOTE: since we only populate one child
181  * then it's expected that only one device will match all the "if" tests in
182  * this function and get to the device_unregister().
183  *
184  * Return: 0 if no error or negative error code.
185  */
186 static int of_dp_aux_ep_destroy(struct device *dev, void *data)
187 {
188 	struct device_node *np = dev->of_node;
189 
190 	if (dev->bus != &dp_aux_bus_type)
191 		return 0;
192 
193 	if (!of_node_check_flag(np, OF_POPULATED))
194 		return 0;
195 
196 	of_node_clear_flag(np, OF_POPULATED);
197 	of_node_put(np);
198 
199 	device_unregister(dev);
200 
201 	return 0;
202 }
203 
204 /**
205  * of_dp_aux_depopulate_bus() - Undo of_dp_aux_populate_bus
206  * @aux: The AUX channel whose device we want to depopulate
207  *
208  * This will destroy the device that was created
209  * by of_dp_aux_populate_bus().
210  */
211 void of_dp_aux_depopulate_bus(struct drm_dp_aux *aux)
212 {
213 	device_for_each_child_reverse(aux->dev, NULL, of_dp_aux_ep_destroy);
214 }
215 EXPORT_SYMBOL_GPL(of_dp_aux_depopulate_bus);
216 
217 /**
218  * of_dp_aux_populate_bus() - Populate the endpoint device on the DP AUX
219  * @aux: The AUX channel whose device we want to populate. It is required that
220  *       drm_dp_aux_init() has already been called for this AUX channel.
221  * @done_probing: Callback functions to call after EP device finishes probing.
222  *                Will not be called if there are no EP devices and this
223  *                function will return -ENODEV.
224  *
225  * This will populate the device (expected to be an eDP panel) under the
226  * "aux-bus" node of the device providing the AUX channel (AKA aux->dev).
227  *
228  * When this function finishes, it is _possible_ (but not guaranteed) that
229  * our sub-device will have finished probing. It should be noted that if our
230  * sub-device returns -EPROBE_DEFER or is probing asynchronously for some
231  * reason that we will not return any error codes ourselves but our
232  * sub-device will _not_ have actually probed successfully yet.
233  *
234  * In many cases it's important for the caller of this function to be notified
235  * when our sub device finishes probing. Our sub device is expected to be an
236  * eDP panel and the caller is expected to be an eDP controller. The eDP
237  * controller needs to be able to get a reference to the panel when it finishes
238  * probing. For this reason the caller can pass in a function pointer that
239  * will be called when our sub-device finishes probing.
240  *
241  * If this function succeeds you should later make sure you call
242  * of_dp_aux_depopulate_bus() to undo it, or just use the devm version
243  * of this function.
244  *
245  * Return: 0 if no error or negative error code; returns -ENODEV if there are
246  *         no children. The done_probing() function won't be called in that
247  *         case.
248  */
249 int of_dp_aux_populate_bus(struct drm_dp_aux *aux,
250 			   int (*done_probing)(struct drm_dp_aux *aux))
251 {
252 	struct device_node *bus = NULL, *np = NULL;
253 	struct dp_aux_ep_device *aux_ep;
254 	struct dp_aux_ep_device_with_data *aux_ep_with_data;
255 	int ret;
256 
257 	/* drm_dp_aux_init() should have been called already; warn if not */
258 	WARN_ON_ONCE(!aux->ddc.algo);
259 
260 	if (!aux->dev->of_node)
261 		return -ENODEV;
262 	bus = of_get_child_by_name(aux->dev->of_node, "aux-bus");
263 	if (!bus)
264 		return -ENODEV;
265 
266 	np = of_get_next_available_child(bus, NULL);
267 	of_node_put(bus);
268 	if (!np)
269 		return -ENODEV;
270 
271 	if (of_node_test_and_set_flag(np, OF_POPULATED)) {
272 		dev_err(aux->dev, "DP AUX EP device already populated\n");
273 		ret = -EINVAL;
274 		goto err_did_get_np;
275 	}
276 
277 	aux_ep_with_data = kzalloc(sizeof(*aux_ep_with_data), GFP_KERNEL);
278 	if (!aux_ep_with_data) {
279 		ret = -ENOMEM;
280 		goto err_did_set_populated;
281 	}
282 
283 	aux_ep_with_data->done_probing = done_probing;
284 
285 	aux_ep = &aux_ep_with_data->aux_ep;
286 	aux_ep->aux = aux;
287 	aux_ep->dev.parent = aux->dev;
288 	aux_ep->dev.bus = &dp_aux_bus_type;
289 	aux_ep->dev.type = &dp_aux_device_type_type;
290 	aux_ep->dev.of_node = of_node_get(np);
291 	dev_set_name(&aux_ep->dev, "aux-%s", dev_name(aux->dev));
292 
293 	ret = device_register(&aux_ep->dev);
294 	if (ret) {
295 		dev_err(aux->dev, "Failed to create AUX EP for %pOF: %d\n", np, ret);
296 
297 		/*
298 		 * As per docs of device_register(), call this instead
299 		 * of kfree() directly for error cases.
300 		 */
301 		put_device(&aux_ep->dev);
302 
303 		goto err_did_set_populated;
304 	}
305 
306 	return 0;
307 
308 err_did_set_populated:
309 	of_node_clear_flag(np, OF_POPULATED);
310 
311 err_did_get_np:
312 	of_node_put(np);
313 
314 	return ret;
315 }
316 EXPORT_SYMBOL_GPL(of_dp_aux_populate_bus);
317 
318 static void of_dp_aux_depopulate_bus_void(void *data)
319 {
320 	of_dp_aux_depopulate_bus(data);
321 }
322 
323 /**
324  * devm_of_dp_aux_populate_bus() - devm wrapper for of_dp_aux_populate_bus()
325  * @aux: The AUX channel whose device we want to populate
326  * @done_probing: Callback functions to call after EP device finishes probing.
327  *                Will not be called if there are no EP devices and this
328  *                function will return -ENODEV.
329  *
330  * Handles freeing w/ devm on the device "aux->dev".
331  *
332  * Return: 0 if no error or negative error code; returns -ENODEV if there are
333  *         no children. The done_probing() function won't be called in that
334  *         case.
335  */
336 int devm_of_dp_aux_populate_bus(struct drm_dp_aux *aux,
337 				int (*done_probing)(struct drm_dp_aux *aux))
338 {
339 	int ret;
340 
341 	ret = of_dp_aux_populate_bus(aux, done_probing);
342 	if (ret)
343 		return ret;
344 
345 	return devm_add_action_or_reset(aux->dev,
346 					of_dp_aux_depopulate_bus_void, aux);
347 }
348 EXPORT_SYMBOL_GPL(devm_of_dp_aux_populate_bus);
349 
350 int __dp_aux_dp_driver_register(struct dp_aux_ep_driver *drv, struct module *owner)
351 {
352 	drv->driver.owner = owner;
353 	drv->driver.bus = &dp_aux_bus_type;
354 
355 	return driver_register(&drv->driver);
356 }
357 EXPORT_SYMBOL_GPL(__dp_aux_dp_driver_register);
358 
359 void dp_aux_dp_driver_unregister(struct dp_aux_ep_driver *drv)
360 {
361 	driver_unregister(&drv->driver);
362 }
363 EXPORT_SYMBOL_GPL(dp_aux_dp_driver_unregister);
364 
365 static int __init dp_aux_bus_init(void)
366 {
367 	int ret;
368 
369 	ret = bus_register(&dp_aux_bus_type);
370 	if (ret)
371 		return ret;
372 
373 	return 0;
374 }
375 
376 static void __exit dp_aux_bus_exit(void)
377 {
378 	bus_unregister(&dp_aux_bus_type);
379 }
380 
381 subsys_initcall(dp_aux_bus_init);
382 module_exit(dp_aux_bus_exit);
383 
384 MODULE_AUTHOR("Douglas Anderson <dianders@chromium.org>");
385 MODULE_DESCRIPTION("DRM DisplayPort AUX bus");
386 MODULE_LICENSE("GPL v2");
387