1// SPDX-License-Identifier: MIT
2
3#include <linux/aperture.h>
4#include <linux/platform_device.h>
5
6#include <drm/drm_aperture.h>
7#include <drm/drm_drv.h>
8#include <drm/drm_print.h>
9
10/**
11 * DOC: overview
12 *
13 * A graphics device might be supported by different drivers, but only one
14 * driver can be active at any given time. Many systems load a generic
15 * graphics drivers, such as EFI-GOP or VESA, early during the boot process.
16 * During later boot stages, they replace the generic driver with a dedicated,
17 * hardware-specific driver. To take over the device the dedicated driver
18 * first has to remove the generic driver. DRM aperture functions manage
19 * ownership of DRM framebuffer memory and hand-over between drivers.
20 *
21 * DRM drivers should call drm_aperture_remove_conflicting_framebuffers()
22 * at the top of their probe function. The function removes any generic
23 * driver that is currently associated with the given framebuffer memory.
24 * If the framebuffer is located at PCI BAR 0, the rsp code looks as in the
25 * example given below.
26 *
27 * .. code-block:: c
28 *
29 * static const struct drm_driver example_driver = {
30 * ...
31 * };
32 *
33 * static int remove_conflicting_framebuffers(struct pci_dev *pdev)
34 * {
35 * resource_size_t base, size;
36 * int ret;
37 *
38 * base = pci_resource_start(pdev, 0);
39 * size = pci_resource_len(pdev, 0);
40 *
41 * return drm_aperture_remove_conflicting_framebuffers(base, size,
42 * &example_driver);
43 * }
44 *
45 * static int probe(struct pci_dev *pdev)
46 * {
47 * int ret;
48 *
49 * // Remove any generic drivers...
50 * ret = remove_conflicting_framebuffers(pdev);
51 * if (ret)
52 * return ret;
53 *
54 * // ... and initialize the hardware.
55 * ...
56 *
57 * drm_dev_register();
58 *
59 * return 0;
60 * }
61 *
62 * PCI device drivers should call
63 * drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
64 * framebuffer apertures automatically. Device drivers without knowledge of
65 * the framebuffer's location shall call drm_aperture_remove_framebuffers(),
66 * which removes all drivers for known framebuffer.
67 *
68 * Drivers that are susceptible to being removed by other drivers, such as
69 * generic EFI or VESA drivers, have to register themselves as owners of their
70 * given framebuffer memory. Ownership of the framebuffer memory is achieved
71 * by calling devm_aperture_acquire_from_firmware(). On success, the driver
72 * is the owner of the framebuffer range. The function fails if the
73 * framebuffer is already owned by another driver. See below for an example.
74 *
75 * .. code-block:: c
76 *
77 * static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
78 * {
79 * resource_size_t base, size;
80 *
81 * mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
82 * if (!mem)
83 * return -EINVAL;
84 * base = mem->start;
85 * size = resource_size(mem);
86 *
87 * return devm_acquire_aperture_from_firmware(dev, base, size);
88 * }
89 *
90 * static int probe(struct platform_device *pdev)
91 * {
92 * struct drm_device *dev;
93 * int ret;
94 *
95 * // ... Initialize the device...
96 * dev = devm_drm_dev_alloc();
97 * ...
98 *
99 * // ... and acquire ownership of the framebuffer.
100 * ret = acquire_framebuffers(dev, pdev);
101 * if (ret)
102 * return ret;
103 *
104 * drm_dev_register(dev, 0);
105 *
106 * return 0;
107 * }
108 *
109 * The generic driver is now subject to forced removal by other drivers. This
110 * only works for platform drivers that support hot unplug.
111 * When a driver calls drm_aperture_remove_conflicting_framebuffers() et al.
112 * for the registered framebuffer range, the aperture helpers call
113 * platform_device_unregister() and the generic driver unloads itself. It
114 * may not access the device's registers, framebuffer memory, ROM, etc
115 * afterwards.
116 */
117
118/**
119 * devm_aperture_acquire_from_firmware - Acquires ownership of a firmware framebuffer
120 * on behalf of a DRM driver.
121 * @dev: the DRM device to own the framebuffer memory
122 * @base: the framebuffer's byte offset in physical memory
123 * @size: the framebuffer size in bytes
124 *
125 * Installs the given device as the new owner of the framebuffer. The function
126 * expects the framebuffer to be provided by a platform device that has been
127 * set up by firmware. Firmware can be any generic interface, such as EFI,
128 * VESA, VGA, etc. If the native hardware driver takes over ownership of the
129 * framebuffer range, the firmware state gets lost. Aperture helpers will then
130 * unregister the platform device automatically. Acquired apertures are
131 * released automatically if the underlying device goes away.
132 *
133 * The function fails if the framebuffer range, or parts of it, is currently
134 * owned by another driver. To evict current owners, callers should use
135 * drm_aperture_remove_conflicting_framebuffers() et al. before calling this
136 * function. The function also fails if the given device is not a platform
137 * device.
138 *
139 * Returns:
140 * 0 on success, or a negative errno value otherwise.
141 */
142int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
143 resource_size_t size)
144{
145 struct platform_device *pdev;
146
147 if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
148 return -EINVAL;
149
150 pdev = to_platform_device(dev->dev);
151
152 return devm_aperture_acquire_for_platform_device(pdev, base, size);
153}
154EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);
155
156/**
157 * drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
158 * @base: the aperture's base address in physical memory
159 * @size: aperture size in bytes
160 * @req_driver: requesting DRM driver
161 *
162 * This function removes graphics device drivers which use the memory range described by
163 * @base and @size.
164 *
165 * Returns:
166 * 0 on success, or a negative errno code otherwise
167 */
168int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
169 const struct drm_driver *req_driver)
170{
171 return aperture_remove_conflicting_devices(base, size, name: req_driver->name);
172}
173EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
174
175/**
176 * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
177 * @pdev: PCI device
178 * @req_driver: requesting DRM driver
179 *
180 * This function removes graphics device drivers using the memory range configured
181 * for any of @pdev's memory bars. The function assumes that a PCI device with
182 * shadowed ROM drives a primary display and so kicks out vga16fb.
183 *
184 * Returns:
185 * 0 on success, or a negative errno code otherwise
186 */
187int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
188 const struct drm_driver *req_driver)
189{
190 return aperture_remove_conflicting_pci_devices(pdev, name: req_driver->name);
191}
192EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);
193

source code of linux/drivers/gpu/drm/drm_aperture.c