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 *		bool primary = false;
 36 *		resource_size_t base, size;
 37 *		int ret;
 38 *
 39 *		base = pci_resource_start(pdev, 0);
 40 *		size = pci_resource_len(pdev, 0);
 41 *	#ifdef CONFIG_X86
 42 *		primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
 43 *	#endif
 44 *
 45 *		return drm_aperture_remove_conflicting_framebuffers(base, size, primary,
 46 *		                                                    &example_driver);
 47 *	}
 48 *
 49 *	static int probe(struct pci_dev *pdev)
 50 *	{
 51 *		int ret;
 52 *
 53 *		// Remove any generic drivers...
 54 *		ret = remove_conflicting_framebuffers(pdev);
 55 *		if (ret)
 56 *			return ret;
 57 *
 58 *		// ... and initialize the hardware.
 59 *		...
 60 *
 61 *		drm_dev_register();
 62 *
 63 *		return 0;
 64 *	}
 65 *
 66 * PCI device drivers should call
 67 * drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
 68 * framebuffer apertures automatically. Device drivers without knowledge of
 69 * the framebuffer's location shall call drm_aperture_remove_framebuffers(),
 70 * which removes all drivers for known framebuffer.
 71 *
 72 * Drivers that are susceptible to being removed by other drivers, such as
 73 * generic EFI or VESA drivers, have to register themselves as owners of their
 74 * given framebuffer memory. Ownership of the framebuffer memory is achieved
 75 * by calling devm_aperture_acquire_from_firmware(). On success, the driver
 76 * is the owner of the framebuffer range. The function fails if the
 77 * framebuffer is already owned by another driver. See below for an example.
 78 *
 79 * .. code-block:: c
 80 *
 81 *	static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
 82 *	{
 83 *		resource_size_t base, size;
 84 *
 85 *		mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 86 *		if (!mem)
 87 *			return -EINVAL;
 88 *		base = mem->start;
 89 *		size = resource_size(mem);
 90 *
 91 *		return devm_acquire_aperture_from_firmware(dev, base, size);
 92 *	}
 93 *
 94 *	static int probe(struct platform_device *pdev)
 95 *	{
 96 *		struct drm_device *dev;
 97 *		int ret;
 98 *
 99 *		// ... Initialize the device...
100 *		dev = devm_drm_dev_alloc();
101 *		...
102 *
103 *		// ... and acquire ownership of the framebuffer.
104 *		ret = acquire_framebuffers(dev, pdev);
105 *		if (ret)
106 *			return ret;
107 *
108 *		drm_dev_register(dev, 0);
109 *
110 *		return 0;
111 *	}
112 *
113 * The generic driver is now subject to forced removal by other drivers. This
114 * only works for platform drivers that support hot unplug.
115 * When a driver calls drm_aperture_remove_conflicting_framebuffers() et al.
116 * for the registered framebuffer range, the aperture helpers call
117 * platform_device_unregister() and the generic driver unloads itself. It
118 * may not access the device's registers, framebuffer memory, ROM, etc
119 * afterwards.
120 */
121
122/**
123 * devm_aperture_acquire_from_firmware - Acquires ownership of a firmware framebuffer
124 *                                       on behalf of a DRM driver.
125 * @dev:	the DRM device to own the framebuffer memory
126 * @base:	the framebuffer's byte offset in physical memory
127 * @size:	the framebuffer size in bytes
128 *
129 * Installs the given device as the new owner of the framebuffer. The function
130 * expects the framebuffer to be provided by a platform device that has been
131 * set up by firmware. Firmware can be any generic interface, such as EFI,
132 * VESA, VGA, etc. If the native hardware driver takes over ownership of the
133 * framebuffer range, the firmware state gets lost. Aperture helpers will then
134 * unregister the platform device automatically. Acquired apertures are
135 * released automatically if the underlying device goes away.
136 *
137 * The function fails if the framebuffer range, or parts of it, is currently
138 * owned by another driver. To evict current owners, callers should use
139 * drm_aperture_remove_conflicting_framebuffers() et al. before calling this
140 * function. The function also fails if the given device is not a platform
141 * device.
142 *
143 * Returns:
144 * 0 on success, or a negative errno value otherwise.
145 */
146int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
147					resource_size_t size)
148{
149	struct platform_device *pdev;
150
151	if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
152		return -EINVAL;
153
154	pdev = to_platform_device(dev->dev);
155
156	return devm_aperture_acquire_for_platform_device(pdev, base, size);
157}
158EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);
159
160/**
161 * drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
162 * @base: the aperture's base address in physical memory
163 * @size: aperture size in bytes
164 * @primary: also kick vga16fb if present
165 * @req_driver: requesting DRM driver
166 *
167 * This function removes graphics device drivers which use the memory range described by
168 * @base and @size.
169 *
170 * Returns:
171 * 0 on success, or a negative errno code otherwise
172 */
173int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
174						 bool primary, const struct drm_driver *req_driver)
175{
176	return aperture_remove_conflicting_devices(base, size, primary, req_driver->name);
177}
178EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
179
180/**
181 * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
182 * @pdev: PCI device
183 * @req_driver: requesting DRM driver
184 *
185 * This function removes graphics device drivers using the memory range configured
186 * for any of @pdev's memory bars. The function assumes that a PCI device with
187 * shadowed ROM drives a primary display and so kicks out vga16fb.
188 *
189 * Returns:
190 * 0 on success, or a negative errno code otherwise
191 */
192int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
193						     const struct drm_driver *req_driver)
194{
195	return aperture_remove_conflicting_pci_devices(pdev, req_driver->name);
196}
197EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);