video/aperture: optionally match the device in sysfb_disable()

In aperture_remove_conflicting_pci_devices(), we currently only
call sysfb_disable() on vga class devices.  This leads to the
following problem when the pimary device is not VGA compatible:

1. A PCI device with a non-VGA class is the boot display
2. That device is probed first and it is not a VGA device so
   sysfb_disable() is not called, but the device resources
   are freed by aperture_detach_platform_device()
3. Non-primary GPU has a VGA class and it ends up calling sysfb_disable()
4. NULL pointer dereference via sysfb_disable() since the resources
   have already been freed by aperture_detach_platform_device() when
   it was called by the other device.

Fix this by passing a device pointer to sysfb_disable() and checking
the device to determine if we should execute it or not.

v2: Fix build when CONFIG_SCREEN_INFO is not set
v3: Move device check into the mutex
    Drop primary variable in aperture_remove_conflicting_pci_devices()
    Drop __init on pci sysfb_pci_dev_is_enabled()

Fixes: 5ae3716 ("video/aperture: Only remove sysfb on the default vga pci device")
Cc: Javier Martinez Canillas <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
Cc: [email protected]
Reviewed-by: Javier Martinez Canillas <[email protected]>
Reviewed-by: Thomas Zimmermann <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: alexdeucher

drivers/firmware/sysfb.c

@@ -39,6 +39,8 @@ static struct platform_device *pd;
 static DEFINE_MUTEX(disable_lock);
 static bool disabled;
 
+static struct device *sysfb_parent_dev(const struct screen_info *si);
+
 static bool sysfb_unregister(void)
 {
 	if (IS_ERR_OR_NULL(pd))
@@ -52,6 +54,7 @@ static bool sysfb_unregister(void)
 
 /**
  * sysfb_disable() - disable the Generic System Framebuffers support
+ * @dev:	the device to check if non-NULL
  *
  * This disables the registration of system framebuffer devices that match the
  * generic drivers that make use of the system framebuffer set up by firmware.
@@ -61,17 +64,21 @@ static bool sysfb_unregister(void)
  * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
  *          against sysfb_init(), that registers a system framebuffer device.
  */
-void sysfb_disable(void)
+void sysfb_disable(struct device *dev)
 {
+	struct screen_info *si = &screen_info;
+
 	mutex_lock(&disable_lock);
-	sysfb_unregister();
-	disabled = true;
+	if (!dev || dev == sysfb_parent_dev(si)) {
+		sysfb_unregister();
+		disabled = true;
+	}
 	mutex_unlock(&disable_lock);
 }
 EXPORT_SYMBOL_GPL(sysfb_disable);
 
 #if defined(CONFIG_PCI)
-static __init bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
+static bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
 {
 	/*
 	 * TODO: Try to integrate this code into the PCI subsystem
@@ -87,13 +94,13 @@ static __init bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
 	return true;
 }
 #else
-static __init bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
+static bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
 {
 	return false;
 }
 #endif
 
-static __init struct device *sysfb_parent_dev(const struct screen_info *si)
+static struct device *sysfb_parent_dev(const struct screen_info *si)
 {
 	struct pci_dev *pdev;
 

drivers/of/platform.c

@@ -592,7 +592,7 @@ static int __init of_platform_default_populate_init(void)
 			 * This can happen for example on DT systems that do EFI
 			 * booting and may provide a GOP handle to the EFI stub.
 			 */
-			sysfb_disable();
+			sysfb_disable(NULL);
 			of_platform_device_create(node, NULL, NULL);
 			of_node_put(node);
 		}

drivers/video/aperture.c

@@ -293,7 +293,7 @@ int aperture_remove_conflicting_devices(resource_size_t base, resource_size_t si
 	 * ask for this, so let's assume that a real driver for the display
 	 * was already probed and prevent sysfb to register devices later.
 	 */
-	sysfb_disable();
+	sysfb_disable(NULL);
 
 	aperture_detach_devices(base, size);
 
@@ -346,15 +346,10 @@ EXPORT_SYMBOL(__aperture_remove_legacy_vga_devices);
  */
 int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *name)
 {
-	bool primary = false;
 	resource_size_t base, size;
 	int bar, ret = 0;
 
-	if (pdev == vga_default_device())
-		primary = true;
-
-	if (primary)
-		sysfb_disable();
+	sysfb_disable(&pdev->dev);
 
 	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
 		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
@@ -370,7 +365,7 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
 	 * that consumes the VGA framebuffer I/O range. Remove this
 	 * device as well.
 	 */
-	if (primary)
+	if (pdev == vga_default_device())
 		ret = __aperture_remove_legacy_vga_devices(pdev);
 
 	return ret;

include/linux/sysfb.h

@@ -58,11 +58,11 @@ struct efifb_dmi_info {
 
 #ifdef CONFIG_SYSFB
 
-void sysfb_disable(void);
+void sysfb_disable(struct device *dev);
 
 #else /* CONFIG_SYSFB */
 
-static inline void sysfb_disable(void)
+static inline void sysfb_disable(struct device *dev)
 {
 }