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![Thierry Reding](/assets/img/avatar_default.png)
Reword some kerneldoc comments for the DRM aperture handling code. Signed-off-by: Thierry Reding <treding@nvidia.com> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Acked-by: Thomas Zimmermann <tzimmermann@suse.de> Link: https://patchwork.freedesktop.org/patch/msgid/20220905162241.391226-1-thierry.reding@gmail.com
197 lines
6.8 KiB
C
197 lines
6.8 KiB
C
// SPDX-License-Identifier: MIT
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#include <linux/aperture.h>
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#include <linux/platform_device.h>
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#include <drm/drm_aperture.h>
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#include <drm/drm_drv.h>
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#include <drm/drm_print.h>
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/**
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* DOC: overview
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*
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* A graphics device might be supported by different drivers, but only one
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* driver can be active at any given time. Many systems load a generic
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* graphics drivers, such as EFI-GOP or VESA, early during the boot process.
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* During later boot stages, they replace the generic driver with a dedicated,
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* hardware-specific driver. To take over the device the dedicated driver
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* first has to remove the generic driver. DRM aperture functions manage
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* ownership of DRM framebuffer memory and hand-over between drivers.
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*
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* DRM drivers should call drm_aperture_remove_conflicting_framebuffers()
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* at the top of their probe function. The function removes any generic
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* driver that is currently associated with the given framebuffer memory.
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* If the framebuffer is located at PCI BAR 0, the rsp code looks as in the
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* example given below.
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*
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* .. code-block:: c
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*
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* static const struct drm_driver example_driver = {
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* ...
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* };
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*
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* static int remove_conflicting_framebuffers(struct pci_dev *pdev)
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* {
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* bool primary = false;
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* resource_size_t base, size;
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* int ret;
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*
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* base = pci_resource_start(pdev, 0);
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* size = pci_resource_len(pdev, 0);
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* #ifdef CONFIG_X86
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* primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
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* #endif
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*
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* return drm_aperture_remove_conflicting_framebuffers(base, size, primary,
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* &example_driver);
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* }
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*
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* static int probe(struct pci_dev *pdev)
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* {
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* int ret;
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*
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* // Remove any generic drivers...
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* ret = remove_conflicting_framebuffers(pdev);
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* if (ret)
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* return ret;
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*
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* // ... and initialize the hardware.
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* ...
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*
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* drm_dev_register();
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*
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* return 0;
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* }
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*
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* PCI device drivers should call
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* drm_aperture_remove_conflicting_pci_framebuffers() and let it detect the
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* framebuffer apertures automatically. Device drivers without knowledge of
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* the framebuffer's location shall call drm_aperture_remove_framebuffers(),
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* which removes all drivers for known framebuffer.
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*
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* Drivers that are susceptible to being removed by other drivers, such as
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* generic EFI or VESA drivers, have to register themselves as owners of their
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* given framebuffer memory. Ownership of the framebuffer memory is achieved
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* by calling devm_aperture_acquire_from_firmware(). On success, the driver
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* is the owner of the framebuffer range. The function fails if the
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* framebuffer is already owned by another driver. See below for an example.
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*
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* .. code-block:: c
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*
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* static int acquire_framebuffers(struct drm_device *dev, struct platform_device *pdev)
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* {
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* resource_size_t base, size;
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*
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* mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
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* if (!mem)
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* return -EINVAL;
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* base = mem->start;
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* size = resource_size(mem);
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*
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* return devm_acquire_aperture_from_firmware(dev, base, size);
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* }
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*
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* static int probe(struct platform_device *pdev)
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* {
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* struct drm_device *dev;
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* int ret;
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*
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* // ... Initialize the device...
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* dev = devm_drm_dev_alloc();
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* ...
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*
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* // ... and acquire ownership of the framebuffer.
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* ret = acquire_framebuffers(dev, pdev);
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* if (ret)
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* return ret;
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*
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* drm_dev_register(dev, 0);
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*
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* return 0;
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* }
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*
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* The generic driver is now subject to forced removal by other drivers. This
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* only works for platform drivers that support hot unplug.
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* When a driver calls drm_aperture_remove_conflicting_framebuffers() et al.
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* for the registered framebuffer range, the aperture helpers call
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* platform_device_unregister() and the generic driver unloads itself. It
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* may not access the device's registers, framebuffer memory, ROM, etc
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* afterwards.
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*/
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/**
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* devm_aperture_acquire_from_firmware - Acquires ownership of a firmware framebuffer
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* on behalf of a DRM driver.
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* @dev: the DRM device to own the framebuffer memory
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* @base: the framebuffer's byte offset in physical memory
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* @size: the framebuffer size in bytes
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*
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* Installs the given device as the new owner of the framebuffer. The function
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* expects the framebuffer to be provided by a platform device that has been
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* set up by firmware. Firmware can be any generic interface, such as EFI,
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* VESA, VGA, etc. If the native hardware driver takes over ownership of the
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* framebuffer range, the firmware state gets lost. Aperture helpers will then
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* unregister the platform device automatically. Acquired apertures are
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* released automatically if the underlying device goes away.
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*
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* The function fails if the framebuffer range, or parts of it, is currently
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* owned by another driver. To evict current owners, callers should use
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* drm_aperture_remove_conflicting_framebuffers() et al. before calling this
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* function. The function also fails if the given device is not a platform
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* device.
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*
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* Returns:
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* 0 on success, or a negative errno value otherwise.
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*/
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int devm_aperture_acquire_from_firmware(struct drm_device *dev, resource_size_t base,
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resource_size_t size)
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{
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struct platform_device *pdev;
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if (drm_WARN_ON(dev, !dev_is_platform(dev->dev)))
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return -EINVAL;
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pdev = to_platform_device(dev->dev);
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return devm_aperture_acquire_for_platform_device(pdev, base, size);
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}
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EXPORT_SYMBOL(devm_aperture_acquire_from_firmware);
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/**
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* drm_aperture_remove_conflicting_framebuffers - remove existing framebuffers in the given range
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* @base: the aperture's base address in physical memory
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* @size: aperture size in bytes
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* @primary: also kick vga16fb if present
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* @req_driver: requesting DRM driver
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*
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* This function removes graphics device drivers which use the memory range described by
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* @base and @size.
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*
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* Returns:
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* 0 on success, or a negative errno code otherwise
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*/
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int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_size_t size,
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bool primary, const struct drm_driver *req_driver)
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{
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return aperture_remove_conflicting_devices(base, size, primary, req_driver->name);
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}
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EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
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/**
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* drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
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* @pdev: PCI device
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* @req_driver: requesting DRM driver
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*
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* This function removes graphics device drivers using the memory range configured
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* for any of @pdev's memory bars. The function assumes that a PCI device with
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* shadowed ROM drives a primary display and so kicks out vga16fb.
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*
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* Returns:
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* 0 on success, or a negative errno code otherwise
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*/
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int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
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const struct drm_driver *req_driver)
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{
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return aperture_remove_conflicting_pci_devices(pdev, req_driver->name);
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}
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EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);
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