video: Provide screen_info_get_pci_dev() to find screen_info's PCI device

Add screen_info_get_pci_dev() to find the PCI device of an instance
of screen_info. Does nothing on systems without PCI bus.

v3:
* search PCI device with pci_get_base_class() (Sui)
v2:
* remove ret from screen_info_pci_dev() (Javier)

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/Makefile

···
 obj-$(CONFIG_HDMI)                += hdmi.o
 
 screen_info-y			  := screen_info_generic.o
+screen_info-$(CONFIG_PCI)         += screen_info_pci.o
 
 obj-$(CONFIG_VT)		  += console/
 obj-$(CONFIG_FB_STI)		  += console/

drivers/video/screen_info_pci.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/pci.h>
+#include <linux/screen_info.h>
+
+static struct pci_dev *__screen_info_pci_dev(struct resource *res)
+{
+	struct pci_dev *pdev = NULL;
+	const struct resource *r = NULL;
+
+	if (!(res->flags & IORESOURCE_MEM))
+		return NULL;
+
+	while (!r && (pdev = pci_get_base_class(PCI_BASE_CLASS_DISPLAY, pdev))) {
+		r = pci_find_resource(pdev, res);
+	}
+
+	return pdev;
+}
+
+/**
+ * screen_info_pci_dev() - Return PCI parent device that contains screen_info's framebuffer
+ * @si: the screen_info
+ *
+ * Returns:
+ * The screen_info's parent device or NULL on success, or a pointer-encoded
+ * errno value otherwise. The value NULL is not an error. It signals that no
+ * PCI device has been found.
+ */
+struct pci_dev *screen_info_pci_dev(const struct screen_info *si)
+{
+	struct resource res[SCREEN_INFO_MAX_RESOURCES];
+	ssize_t i, numres;
+
+	numres = screen_info_resources(si, res, ARRAY_SIZE(res));
+	if (numres < 0)
+		return ERR_PTR(numres);
+
+	for (i = 0; i < numres; ++i) {
+		struct pci_dev *pdev = __screen_info_pci_dev(&res[i]);
+
+		if (pdev)
+			return pdev;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL(screen_info_pci_dev);

include/linux/screen_info.h

···
  */
 #define SCREEN_INFO_MAX_RESOURCES	3
 
+struct pci_dev;
 struct resource;
 
 static inline bool __screen_info_has_lfb(unsigned int type)
···
 }
 
 ssize_t screen_info_resources(const struct screen_info *si, struct resource *r, size_t num);
+
+#if defined(CONFIG_PCI)
+struct pci_dev *screen_info_pci_dev(const struct screen_info *si);
+#else
+static inline struct pci_dev *screen_info_pci_dev(const struct screen_info *si)
+{
+	return NULL;
+}
+#endif
 
 extern struct screen_info screen_info;