[-next 1/5] PCI: Add the pci_is_vga() helper

[Sui Jingfeng <sui.jingfeng@linux.dev>]

From: Sui Jingfeng <suijingfeng@loongson.cn>

The PCI code and ID assignment specification defined four types of
display controllers for the display base class(03h), and the devices
with 0x00h sub-class code are VGA devices. VGA devices with programming
interface 0x00 is VGA-compatible, VGA devices with programming interface
0x01 are 8514-compatible controllers. Besides, PCI_CLASS_NOT_DEFINED_VGA
is defined to provide backward compatibility for devices that were built
before the class code field was defined. Hence, introduce the pci_is_vga()
helper, let it handle the details for us. It returns true if the PCI(e)
device being tested belongs to the VGA devices category.

Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
---
 include/linux/pci.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index cf6e0b057752..ace727001911 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -713,6 +713,33 @@ static inline bool pci_is_bridge(struct pci_dev *dev)
 		dev->hdr_type == PCI_HEADER_TYPE_CARDBUS;
 }
 
+/**
+ * The PCI code and ID assignment specification defined four types of
+ * display controllers for the display base class(03h), and the devices
+ * with 0x00h sub-class code are VGA devices. VGA devices with programming
+ * interface 0x00 is VGA-compatible, VGA devices with programming interface
+ * 0x01 are 8514-compatible controllers. Besides, PCI_CLASS_NOT_DEFINED_VGA
+ * is defined to provide backward compatibility for devices that were built
+ * before the class code field was defined. This means that it belong to the
+ * VGA devices category also.
+ *
+ * Returns:
+ * true if the PCI device is a VGA device, false otherwise.
+ */
+static inline bool pci_is_vga(struct pci_dev *pdev)
+{
+	if (!pdev)
+		return false;
+
+	if ((pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA)
+		return true;
+
+	if ((pdev->class >> 8) == PCI_CLASS_NOT_DEFINED_VGA)
+		return true;
+
+	return false;
+}
+
 #define for_each_pci_bridge(dev, bus)				\
 	list_for_each_entry(dev, &bus->devices, bus_list)	\
 		if (!pci_is_bridge(dev)) {} else
-- 
2.34.1