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 int dp_aux_ep_dev_modalias(const struct device *dev, struct kobj_uevent_env *env)
165 {
166 	return of_device_uevent_modalias(dev, env);
167 }
168 
169 static struct device_type dp_aux_device_type_type = {
170 	.groups		= dp_aux_ep_dev_groups,
171 	.uevent		= dp_aux_ep_dev_modalias,
172 	.release	= dp_aux_ep_dev_release,
173 };
174 
175 /**
176  * of_dp_aux_ep_destroy() - Destroy an DP AUX endpoint device
177  * @dev: The device to destroy.
178  * @data: Not used
179  *
180  * This is just used as a callback by of_dp_aux_depopulate_bus() and
181  * is called for _all_ of the child devices of the device providing the AUX bus.
182  * We'll only act on those that are of type "dp_aux_bus_type".
183  *
184  * This function is effectively an inverse of what's in
185  * of_dp_aux_populate_bus(). NOTE: since we only populate one child
186  * then it's expected that only one device will match all the "if" tests in
187  * this function and get to the device_unregister().
188  *
189  * Return: 0 if no error or negative error code.
190  */
191 static int of_dp_aux_ep_destroy(struct device *dev, void *data)
192 {
193 	struct device_node *np = dev->of_node;
194 
195 	if (dev->bus != &dp_aux_bus_type)
196 		return 0;
197 
198 	if (!of_node_check_flag(np, OF_POPULATED))
199 		return 0;
200 
201 	of_node_clear_flag(np, OF_POPULATED);
202 	of_node_put(np);
203 
204 	device_unregister(dev);
205 
206 	return 0;
207 }
208 
209 /**
210  * of_dp_aux_depopulate_bus() - Undo of_dp_aux_populate_bus
211  * @aux: The AUX channel whose device we want to depopulate
212  *
213  * This will destroy the device that was created
214  * by of_dp_aux_populate_bus().
215  */
216 void of_dp_aux_depopulate_bus(struct drm_dp_aux *aux)
217 {
218 	device_for_each_child_reverse(aux->dev, NULL, of_dp_aux_ep_destroy);
219 }
220 EXPORT_SYMBOL_GPL(of_dp_aux_depopulate_bus);
221 
222 /**
223  * of_dp_aux_populate_bus() - Populate the endpoint device on the DP AUX
224  * @aux: The AUX channel whose device we want to populate. It is required that
225  *       drm_dp_aux_init() has already been called for this AUX channel.
226  * @done_probing: Callback functions to call after EP device finishes probing.
227  *                Will not be called if there are no EP devices and this
228  *                function will return -ENODEV.
229  *
230  * This will populate the device (expected to be an eDP panel) under the
231  * "aux-bus" node of the device providing the AUX channel (AKA aux->dev).
232  *
233  * When this function finishes, it is _possible_ (but not guaranteed) that
234  * our sub-device will have finished probing. It should be noted that if our
235  * sub-device returns -EPROBE_DEFER or is probing asynchronously for some
236  * reason that we will not return any error codes ourselves but our
237  * sub-device will _not_ have actually probed successfully yet.
238  *
239  * In many cases it's important for the caller of this function to be notified
240  * when our sub device finishes probing. Our sub device is expected to be an
241  * eDP panel and the caller is expected to be an eDP controller. The eDP
242  * controller needs to be able to get a reference to the panel when it finishes
243  * probing. For this reason the caller can pass in a function pointer that
244  * will be called when our sub-device finishes probing.
245  *
246  * If this function succeeds you should later make sure you call
247  * of_dp_aux_depopulate_bus() to undo it, or just use the devm version
248  * of this function.
249  *
250  * Return: 0 if no error or negative error code; returns -ENODEV if there are
251  *         no children. The done_probing() function won't be called in that
252  *         case.
253  */
254 int of_dp_aux_populate_bus(struct drm_dp_aux *aux,
255 			   int (*done_probing)(struct drm_dp_aux *aux))
256 {
257 	struct device_node *bus = NULL, *np = NULL;
258 	struct dp_aux_ep_device *aux_ep;
259 	struct dp_aux_ep_device_with_data *aux_ep_with_data;
260 	int ret;
261 
262 	/* drm_dp_aux_init() should have been called already; warn if not */
263 	WARN_ON_ONCE(!aux->ddc.algo);
264 
265 	if (!aux->dev->of_node)
266 		return -ENODEV;
267 	bus = of_get_child_by_name(aux->dev->of_node, "aux-bus");
268 	if (!bus)
269 		return -ENODEV;
270 
271 	np = of_get_next_available_child(bus, NULL);
272 	of_node_put(bus);
273 	if (!np)
274 		return -ENODEV;
275 
276 	if (of_node_test_and_set_flag(np, OF_POPULATED)) {
277 		dev_err(aux->dev, "DP AUX EP device already populated\n");
278 		ret = -EINVAL;
279 		goto err_did_get_np;
280 	}
281 
282 	aux_ep_with_data = kzalloc(sizeof(*aux_ep_with_data), GFP_KERNEL);
283 	if (!aux_ep_with_data) {
284 		ret = -ENOMEM;
285 		goto err_did_set_populated;
286 	}
287 
288 	aux_ep_with_data->done_probing = done_probing;
289 
290 	aux_ep = &aux_ep_with_data->aux_ep;
291 	aux_ep->aux = aux;
292 	aux_ep->dev.parent = aux->dev;
293 	aux_ep->dev.bus = &dp_aux_bus_type;
294 	aux_ep->dev.type = &dp_aux_device_type_type;
295 	aux_ep->dev.of_node = of_node_get(np);
296 	dev_set_name(&aux_ep->dev, "aux-%s", dev_name(aux->dev));
297 
298 	ret = device_register(&aux_ep->dev);
299 	if (ret) {
300 		dev_err(aux->dev, "Failed to create AUX EP for %pOF: %d\n", np, ret);
301 
302 		/*
303 		 * As per docs of device_register(), call this instead
304 		 * of kfree() directly for error cases.
305 		 */
306 		put_device(&aux_ep->dev);
307 
308 		goto err_did_set_populated;
309 	}
310 
311 	return 0;
312 
313 err_did_set_populated:
314 	of_node_clear_flag(np, OF_POPULATED);
315 
316 err_did_get_np:
317 	of_node_put(np);
318 
319 	return ret;
320 }
321 EXPORT_SYMBOL_GPL(of_dp_aux_populate_bus);
322 
323 static void of_dp_aux_depopulate_bus_void(void *data)
324 {
325 	of_dp_aux_depopulate_bus(data);
326 }
327 
328 /**
329  * devm_of_dp_aux_populate_bus() - devm wrapper for of_dp_aux_populate_bus()
330  * @aux: The AUX channel whose device we want to populate
331  * @done_probing: Callback functions to call after EP device finishes probing.
332  *                Will not be called if there are no EP devices and this
333  *                function will return -ENODEV.
334  *
335  * Handles freeing w/ devm on the device "aux->dev".
336  *
337  * Return: 0 if no error or negative error code; returns -ENODEV if there are
338  *         no children. The done_probing() function won't be called in that
339  *         case.
340  */
341 int devm_of_dp_aux_populate_bus(struct drm_dp_aux *aux,
342 				int (*done_probing)(struct drm_dp_aux *aux))
343 {
344 	int ret;
345 
346 	ret = of_dp_aux_populate_bus(aux, done_probing);
347 	if (ret)
348 		return ret;
349 
350 	return devm_add_action_or_reset(aux->dev,
351 					of_dp_aux_depopulate_bus_void, aux);
352 }
353 EXPORT_SYMBOL_GPL(devm_of_dp_aux_populate_bus);
354 
355 int __dp_aux_dp_driver_register(struct dp_aux_ep_driver *drv, struct module *owner)
356 {
357 	drv->driver.owner = owner;
358 	drv->driver.bus = &dp_aux_bus_type;
359 
360 	return driver_register(&drv->driver);
361 }
362 EXPORT_SYMBOL_GPL(__dp_aux_dp_driver_register);
363 
364 void dp_aux_dp_driver_unregister(struct dp_aux_ep_driver *drv)
365 {
366 	driver_unregister(&drv->driver);
367 }
368 EXPORT_SYMBOL_GPL(dp_aux_dp_driver_unregister);
369 
370 static int __init dp_aux_bus_init(void)
371 {
372 	int ret;
373 
374 	ret = bus_register(&dp_aux_bus_type);
375 	if (ret)
376 		return ret;
377 
378 	return 0;
379 }
380 
381 static void __exit dp_aux_bus_exit(void)
382 {
383 	bus_unregister(&dp_aux_bus_type);
384 }
385 
386 subsys_initcall(dp_aux_bus_init);
387 module_exit(dp_aux_bus_exit);
388 
389 MODULE_AUTHOR("Douglas Anderson <dianders@chromium.org>");
390 MODULE_DESCRIPTION("DRM DisplayPort AUX bus");
391 MODULE_LICENSE("GPL v2");
392