[PATCH 5.15 106/135] PCI: pci-bridge-emul: Add description for class_revision field

[Greg Kroah-Hartman]

From: Pali Roh�<pali@xxxxxxxxxx>

commit 9319230ac147067652b58fe849ffe0ceec098665 upstream.

The current assignment to the class_revision member

  class_revision |= cpu_to_le32(PCI_CLASS_BRIDGE_PCI << 16);

can make the reader think that class is at high 16 bits of the member and
revision at low 16 bits.

In reality, class is at high 24 bits, but the class for PCI Bridge Normal
Decode is PCI_CLASS_BRIDGE_PCI << 8.

Change the assignment and add a comment to make this clearer.

Link: https://lore.kernel.org/r/20211130172913.9727-2-kabel@xxxxxxxxxx
Signed-off-by: Pali Roh�<pali@xxxxxxxxxx>
Signed-off-by: Marek Beh�abel@xxxxxxxxxx>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Signed-off-by: Marek Beh�abel@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/pci-bridge-emul.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/pci/pci-bridge-emul.c
+++ b/drivers/pci/pci-bridge-emul.c
@@ -284,7 +284,11 @@ int pci_bridge_emul_init(struct pci_brid
 {
 	BUILD_BUG_ON(sizeof(bridge->conf) != PCI_BRIDGE_CONF_END);
 
-	bridge->conf.class_revision |= cpu_to_le32(PCI_CLASS_BRIDGE_PCI << 16);
+	/*
+	 * class_revision: Class is high 24 bits and revision is low 8 bit of this member,
+	 * while class for PCI Bridge Normal Decode has the 24-bit value: PCI_CLASS_BRIDGE_PCI << 8
+	 */
+	bridge->conf.class_revision |= cpu_to_le32((PCI_CLASS_BRIDGE_PCI << 8) << 8);
 	bridge->conf.header_type = PCI_HEADER_TYPE_BRIDGE;
 	bridge->conf.cache_line_size = 0x10;
 	bridge->conf.status = cpu_to_le16(PCI_STATUS_CAP_LIST);