linux-kernel - [PATCH 10/15] PCI: mvebu: Set PCI Bridge Class Code to PCI Bridge

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Date:   Thu, 25 Nov 2021 13:46:00 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marek Behún <kabel@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 10/15] PCI: mvebu: Set PCI Bridge Class Code to PCI Bridge

The default value of Class Code of this bridge corresponds to a Memory
controller, though. This is probably relict from the past when old
Marvell/Galileo PCI-based controllers were used as standalone PCI device
for connecting SDRAM or workaround for PCs with broken BIOS. Details are
in commit 36de23a4c5f0 ("MIPS: Cobalt: Explain GT64111 early PCI fixup").

Change the Class Code to correspond to a PCI Bridge.

Add comment explaining this change.

Signed-off-by: Pali Rohár <pali@...nel.org>
Cc: stable@...r.kernel.org
---
 drivers/pci/controller/pci-mvebu.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
index 017ae9f869ac..4edce441901c 100644
--- a/drivers/pci/controller/pci-mvebu.c
+++ b/drivers/pci/controller/pci-mvebu.c
@@ -225,7 +225,7 @@ static void mvebu_pcie_setup_wins(struct mvebu_pcie_port *port)
 
 static void mvebu_pcie_setup_hw(struct mvebu_pcie_port *port)
 {
-	u32 ctrl, cmd, mask;
+	u32 ctrl, cmd, dev_rev, mask;
 
 	/* Setup PCIe controller to Root Complex mode. */
 	ctrl = mvebu_readl(port, PCIE_CTRL_OFF);
@@ -237,6 +237,32 @@ static void mvebu_pcie_setup_hw(struct mvebu_pcie_port *port)
 	cmd &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
 	mvebu_writel(port, cmd, PCIE_CMD_OFF);
 
+	/*
+	 * Change Class Code of PCI Bridge device to PCI Bridge (0x6004)
+	 * because default value is Memory controller (0x5080).
+	 *
+	 * Note that this mvebu PCI Bridge does not have compliant Type 1
+	 * Configuration Space. Header Type is reported as Type 0 and it
+	 * has format of Type 0 config space.
+	 *
+	 * Moreover Type 0 BAR registers (ranges 0x10 - 0x28 and 0x30 - 0x34)
+	 * have the same format in Marvell's specification as in PCIe
+	 * specification, but their meaning is totally different and they do
+	 * different things: they are aliased into internal mvebu registers
+	 * (e.g. PCIE_BAR_LO_OFF) and these should not be changed or
+	 * reconfigured by pci device drivers.
+	 *
+	 * Therefore driver uses emulation of PCI Bridge which emulates
+	 * access to configuration space via internal mvebu registers or
+	 * emulated configuration buffer. Driver access these PCI Bridge
+	 * directly for simplification, but these registers can be accessed
+	 * also via standard mvebu way for accessing PCI config space.
+	 */
+	dev_rev = mvebu_readl(port, PCIE_DEV_REV_OFF);
+	dev_rev &= ~0xffffff00;
+	dev_rev |= (PCI_CLASS_BRIDGE_PCI << 8) << 8;
+	mvebu_writel(port, dev_rev, PCIE_DEV_REV_OFF);
+
 	/* Point PCIe unit MBUS decode windows to DRAM space. */
 	mvebu_pcie_setup_wins(port);
 
-- 
2.20.1