linux/drivers/gpu/drm/drm_aperture.c

// SPDX-License-Identifier: MIT

#include <linux/aperture.h>
#include <linux/platform_device.h>

#include <drm/drm_aperture.h>
#include <drm/drm_drv.h>
#include <drm/drm_print.h>

/**
 * DOC: overview
 *
 * A graphics device might be supported by different drivers, but only one
 * driver can be active at any given time. Many systems load a generic
 * graphics drivers, such as EFI-GOP or VESA, early during the boot process.
 * During later boot stages, they replace the generic driver with a dedicated,
 * hardware-specific driver. To take over the device the dedicated driver
 * first has to remove the generic driver. DRM aperture functions manage
 * ownership of DRM framebuffer memory and hand-over between drivers.
 *
 * DRM drivers should call drm_aperture_remove_conflicting_framebuffers()
 * at the top of their probe function. The function removes any generic
 * driver that is currently associated with the given framebuffer memory.
 * If the framebuffer is located at PCI BAR 0, the rsp code looks as in the
 * example given below.
 *
 * .. code-block:: c
 *
 *	static const struct drm_driver example_driver = {
 *		...
 *	};
 *
 *	static int remove_conflicting_framebuffers(struct pci_dev *pdev)
 *	{
 *		resource_size_t base, size;
 *		int ret;
 *
 *		base = pci_resource_start(pdev, 0);
 *		size = pci_resource_len(pdev, 0);
 *
 *		return drm_aperture_remove_conflicting_framebuffers(base, size,
 *		                                                    &example_driver);
 *	}
 *
 *	static int probe(struct pci_dev *pdev)
 *	{
 *		int ret;
 *
 *		// Remove any generic drivers...
 *		ret = remove_conflicting_framebuffers(pdev);
 *		if (ret)
 *			return ret;
 *
 *		// ... and initialize the hardware.
 *		...
 *
 *		drm_dev_register();
 *
 *		return 0;
 *	}
 *
 * PCI device drivers should call
 * drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
 * framebuffer apertures automatically. Device drivers without knowledge of
 * the framebuffer's location shall call drm_aperture_remove_framebuffers(),
 * which removes all drivers for known framebuffer.
 *
 * Drivers that are susceptible to being removed by other drivers, such as
 * generic EFI or VESA drivers, have to register themselves as owners of their
 * given framebuffer memory. Ownership of the framebuffer memory is achieved
 * by calling devm_aperture_acquire_from_firmware(). On success, the driver
 * is the owner of the framebuffer range. The function fails if the
 * framebuffer is already owned by another driver. See below for an example.
 *
 * .. code-block:: c
 *
 *	static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
 *	{
 *		resource_size_t base, size;
 *
 *		mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 *		if (!mem)
 *			return -EINVAL;
 *		base = mem->start;
 *		size = resource_size(mem);
 *
 *		return devm_acquire_aperture_from_firmware(dev, base, size);
 *	}
 *
 *	static int probe(struct platform_device *pdev)
 *	{
 *		struct drm_device *dev;
 *		int ret;
 *
 *		// ... Initialize the device...
 *		dev = devm_drm_dev_alloc();
 *		...
 *
 *		// ... and acquire ownership of the framebuffer.
 *		ret = acquire_framebuffers(dev, pdev);
 *		if (ret)
 *			return ret;
 *
 *		drm_dev_register(dev, 0);
 *
 *		return 0;
 *	}
 *
 * The generic driver is now subject to forced removal by other drivers. This
 * only works for platform drivers that support hot unplug.
 * When a driver calls drm_aperture_remove_conflicting_framebuffers() et al.
 * for the registered framebuffer range, the aperture helpers call
 * platform_device_unregister() and the generic driver unloads itself. It
 * may not access the device's registers, framebuffer memory, ROM, etc
 * afterwards.
 */

/**
 * devm_aperture_acquire_from_firmware - Acquires ownership of a firmware framebuffer
 *                                       on behalf of a DRM driver.
 * @dev:	the DRM device to own the framebuffer memory
 * @base:	the framebuffer's byte offset in physical memory
 * @size:	the framebuffer size in bytes
 *
 * Installs the given device as the new owner of the framebuffer. The function
 * expects the framebuffer to be provided by a platform device that has been
 * set up by firmware. Firmware can be any generic interface, such as EFI,
 * VESA, VGA, etc. If the native hardware driver takes over ownership of the
 * framebuffer range, the firmware state gets lost. Aperture helpers will then
 * unregister the platform device automatically. Acquired apertures are
 * released automatically if the underlying device goes away.
 *
 * The function fails if the framebuffer range, or parts of it, is currently
 * owned by another driver. To evict current owners, callers should use
 * drm_aperture_remove_conflicting_framebuffers() et al. before calling this
 * function. The function also fails if the given device is not a platform
 * device.
 *
 * Returns:
 * 0 on success, or a negative errno value otherwise.
 */
int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
					resource_size_t size)
{
	struct platform_device *pdev;

	if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
		return -EINVAL;

	pdev = to_platform_device(dev->dev);

	return devm_aperture_acquire_for_platform_device(pdev, base, size);
}
EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);

/**
 * drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
 * @base: the aperture's base address in physical memory
 * @size: aperture size in bytes
 * @req_driver: requesting DRM driver
 *
 * This function removes graphics device drivers which use the memory range described by
 * @base and @size.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise
 */
int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
						 const struct drm_driver *req_driver)
{
	return aperture_remove_conflicting_devices(base, size, req_driver->name);
}
EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);

/**
 * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
 * @pdev: PCI device
 * @req_driver: requesting DRM driver
 *
 * This function removes graphics device drivers using the memory range configured
 * for any of @pdev's memory bars. The function assumes that a PCI device with
 * shadowed ROM drives a primary display and so kicks out vga16fb.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise
 */
int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
						     const struct drm_driver *req_driver)
{
	return aperture_remove_conflicting_pci_devices(pdev, req_driver->name);
}
EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);