diff mbox series

[5.15,01/30] PCI: pci-bridge-emul: Add description for class_revision field

Message ID 20220504165755.30002-2-kabel@kernel.org
State New
Headers show
Series PCIe Aardvark controller backports for 5.15 | expand

Commit Message

Marek Behún May 4, 2022, 4:57 p.m. UTC 
From: Pali Rohár <pali@kernel.org>

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@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Marek Behún <kabel@kernel.org>
---
 drivers/pci/pci-bridge-emul.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/drivers/pci/pci-bridge-emul.c b/drivers/pci/pci-bridge-emul.c
index 37504c2cce9b..0a4e71301537 100644
--- 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_bridge_emul *bridge,
 {
 	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);