1 files changed, 114 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_aperture.c b/drivers/gpu/drm/drm_aperture.c
new file mode 100644
index 000000000000..929dcbc0758a
--- /dev/null
+++ b/drivers/gpu/drm/drm_aperture.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: MIT
+
+#include <drm/drm_aperture.h>
+#include <drm/drm_fb_helper.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 int remove_conflicting_framebuffers(struct pci_dev *pdev)
+ *	{
+ *		bool primary = false;
+ *		resource_size_t base, size;
+ *		int ret;
+ *
+ *		base = pci_resource_start(pdev, 0);
+ *		size = pci_resource_len(pdev, 0);
+ *	#ifdef CONFIG_X86
+ *		primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
+ *	#endif
+ *
+ *		return drm_aperture_remove_conflicting_framebuffers(base, size, primary,
+ *		                                                    "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.
+ */
+
+/**
+ * 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
+ * @primary: also kick vga16fb if present
+ * @name: requesting driver name
+ *
+ * This function removes graphics device drivers which use 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,
+						 bool primary, const char *name)
+{
+	struct apertures_struct *a;
+	int ret;
+
+	a = alloc_apertures(1);
+	if (!a)
+		return -ENOMEM;
+
+	a->ranges[0].base = base;
+	a->ranges[0].size = size;
+
+	ret = drm_fb_helper_remove_conflicting_framebuffers(a, name, primary);
+	kfree(a);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
+
+/**
+ * drm_aperture_remove_conflicting_pci_framebuffers - remove existing framebuffers for PCI devices
+ * @pdev: PCI device
+ * @name: requesting driver name
+ *
+ * This function removes graphics device drivers using memory range configured
+ * for any of @pdev's memory bars. The function assumes that 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 char *name)
+{
+	return drm_fb_helper_remove_conflicting_pci_framebuffers(pdev, name);
+}
+EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);