video/aperture: Provide a VGA helper for gma500 and internal use

The hardware for gma500 is different from the rest, as it uses stolen
framebuffer memory that is not available via PCI BAR. The regular PCI
removal helper cannot detect the framebuffer, while the non-PCI helper
misses possible conflicting VGA devices (i.e., a framebuffer or text
console).

Gma500 therefore calls both helpers to catch all cases. It's confusing
as it implies that there's something about the PCI device that requires
ownership management. The relationship between the PCI device and the
VGA devices is non-obvious. At worst, readers might assume that calling
two functions for clearing aperture ownership is a bug in the driver.

Hence, move the PCI removal helper's code for VGA functionality into
a separate function and call this function from gma500. Documents the
purpose of each call to aperture helpers. The change contains comments
and example code form the discussion at [1].

v5:
	* fix grammar in gma500 comment (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230404201842.567344-1-daniel.vetter@ffwll.ch/ # 1
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230406132109.32050-10-tzimmermann@suse.de

1 files changed, 40 insertions, 18 deletions

diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
index fa71f8257eed..561be8feca96 100644
--- a/drivers/video/aperture.c
+++ b/drivers/video/aperture.c
@@ -302,6 +302,37 @@ int aperture_remove_conflicting_devices(resource_size_t base, resource_size_t si
 EXPORT_SYMBOL(aperture_remove_conflicting_devices);
 
 /**
+ * __aperture_remove_legacy_vga_devices - remove legacy VGA devices of a PCI devices
+ * @pdev: PCI device
+ *
+ * This function removes VGA devices provided by @pdev, such as a VGA
+ * framebuffer or a console. This is useful if you have a VGA-compatible
+ * PCI graphics device with framebuffers in non-BAR locations. Drivers
+ * should acquire ownership of those memory areas and afterwards call
+ * this helper to release remaining VGA devices.
+ *
+ * If your hardware has its framebuffers accessible via PCI BARS, use
+ * aperture_remove_conflicting_pci_devices() instead. The function will
+ * release any VGA devices automatically.
+ *
+ * WARNING: Apparently we must remove graphics drivers before calling
+ *          this helper. Otherwise the vga fbdev driver falls over if
+ *          we have vgacon configured.
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise
+ */
+int __aperture_remove_legacy_vga_devices(struct pci_dev *pdev)
+{
+	/* VGA framebuffer */
+	aperture_detach_devices(VGA_FB_PHYS_BASE, VGA_FB_PHYS_SIZE);
+
+	/* VGA textmode console */
+	return vga_remove_vgacon(pdev);
+}
+EXPORT_SYMBOL(__aperture_remove_legacy_vga_devices);
+
+/**
  * aperture_remove_conflicting_pci_devices - remove existing framebuffers for PCI devices
  * @pdev: PCI device
  * @name: a descriptive name of the requesting driver
@@ -317,7 +348,7 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
 {
 	bool primary = false;
 	resource_size_t base, size;
-	int bar, ret;
+	int bar, ret = 0;
 
 	if (pdev == vga_default_device())
 		primary = true;
@@ -334,24 +365,15 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
 		aperture_detach_devices(base, size);
 	}
 
-	if (primary) {
-		/*
-		 * If this is the primary adapter, there could be a VGA device
-		 * that consumes the VGA framebuffer I/O range. Remove this
-		 * device as well.
-		 */
-		aperture_detach_devices(VGA_FB_PHYS_BASE, VGA_FB_PHYS_SIZE);
-
-		/*
-		 * WARNING: Apparently we must kick fbdev drivers before vgacon,
-		 * otherwise the vga fbdev driver falls over.
-		 */
-		ret = vga_remove_vgacon(pdev);
-		if (ret)
-			return ret;
-	}
+	/*
+	 * If this is the primary adapter, there could be a VGA device
+	 * that consumes the VGA framebuffer I/O range. Remove this
+	 * device as well.
+	 */
+	if (primary)
+		ret = __aperture_remove_legacy_vga_devices(pdev);
 
-	return 0;
+	return ret;
 
 }
 EXPORT_SYMBOL(aperture_remove_conflicting_pci_devices);