firmware/sysfb: Create firmware device only for enabled PCI devices

Test if the firmware framebuffer's parent PCI device, if any, has
been enabled. If not, the firmware framebuffer is most likely not
working. Hence, do not create a device for the firmware framebuffer
on disabled PCI devices.

So far, efifb tracked the status of the PCI parent device internally
and did not bind if it was disabled. This patch implements the
functionality for all PCI-based firmware framebuffers.

v3:
	* make commit message more precise (Sui)
v2:
	* rework sysfb_pci_dev_is_enabled() (Javier)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212090736.11464-6-tzimmermann@suse.de

drivers/firmware/sysfb.c

@@ -70,15 +70,41 @@ void sysfb_disable(void)
 }
 EXPORT_SYMBOL_GPL(sysfb_disable);
 
+#if defined(CONFIG_PCI)
+static __init bool sysfb_pci_dev_is_enabled(struct pci_dev *pdev)
+{
+	/*
+	 * TODO: Try to integrate this code into the PCI subsystem
+	 */
+	int ret;
+	u16 command;
+
+	ret = pci_read_config_word(pdev, PCI_COMMAND, &command);
+	if (ret != PCIBIOS_SUCCESSFUL)
+		return false;
+	if (!(command & PCI_COMMAND_MEMORY))
+		return false;
+	return true;
+}
+#else
+static __init 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)
 {
 	struct pci_dev *pdev;
 
 	pdev = screen_info_pci_dev(si);
-	if (IS_ERR(pdev))
+	if (IS_ERR(pdev)) {
 		return ERR_CAST(pdev);
-	else if (pdev)
+	} else if (pdev) {
+		if (!sysfb_pci_dev_is_enabled(pdev))
+			return ERR_PTR(-ENODEV);
 		return &pdev->dev;
+	}
 
 	return NULL;
 }
@@ -99,6 +125,8 @@ static __init int sysfb_init(void)
 	sysfb_apply_efi_quirks();
 
 	parent = sysfb_parent_dev(si);
+	if (IS_ERR(parent))
+		goto unlock_mutex;
 
 	/* try to create a simple-framebuffer device */
 	compatible = sysfb_parse_mode(si, &mode);