[PATCH v2] PCI: tegra264: Fix Link Capabilities register offset

[Bjorn Helgaas <helgaas@kernel.org>]

The PCI Express Capability begins at 0x48.  Link Capabilities is a 32-bit
register at offset 0xc, and Link Status is a 16-bit register at offset
0x12:

  Link Capabilities is at 0x48 + 0xc  = 0x54
  Link Status       is at 0x48 + 0x12 = 0x5a

Previously the driver read Link Capabilities with a 16-bit read from
XTL_RC_PCIE_CFG_LINK_CAPS (0x56), which incorrectly read just the upper
half of the register.  When a hotplug-capable port has no link during
probe, tegra264_pcie_icc_set() consequently derives the maximum speed and
width from unrelated bits and requests the wrong interconnect bandwidth.

Correct the Link Capabilities usage by adding a XTL_RC_PCIE_CAP definition
for the base of the PCIe Capability, using the existing PCI_EXP_LNKCAP
(0xc) and PCI_EXP_LNKSTA (0x12) offsets so they're easily searchable, and
reading the entire 32 bits of Link Capabilities.

Fixes: 01c3c27a0ef6 ("PCI: tegra264: Add Tegra264 support")
Based-on-patch-by: Linmao Li <lilinmao@kylinos.cn>
Link: https://lore.kernel.org/20260827093919.2825467-1-lilinmao@kylinos.cn
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---

This fixes a real bug, so I'd like to get this in pci/next for v7.4.  I
can't test this though, so need a review and test from somebody with the
hardware.

 drivers/pci/controller/pcie-tegra264.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/controller/pcie-tegra264.c b/drivers/pci/controller/pcie-tegra264.c
index 653136db401e..c97576ab4a31 100644
--- a/drivers/pci/controller/pcie-tegra264.c
+++ b/drivers/pci/controller/pcie-tegra264.c
@@ -49,8 +49,7 @@
 #define XAL_RC_BAR_CNTL_STANDARD_64B_BAR_EN	BIT(2)
 
 /* XTL registers */
-#define XTL_RC_PCIE_CFG_LINK_CAPS		0x56
-#define XTL_RC_PCIE_CFG_LINK_STATUS		0x5a
+#define XTL_RC_PCIE_CAP				0x48	/* PCIe Capability */
 
 #define XTL_RC_MGMT_PERST_CONTROL		0x218
 #define XTL_RC_MGMT_PERST_CONTROL_PERST_O_N	BIT(0)
@@ -118,11 +117,11 @@ static void tegra264_pcie_icc_set(struct tegra264_pcie *pcie)
 	 * possible, so this is as good as it gets for now.
 	 */
 	if (pcie->link_up) {
-		value = readw(pcie->ecam + XTL_RC_PCIE_CFG_LINK_STATUS);
+		value = readw(pcie->ecam + XTL_RC_PCIE_CAP + PCI_EXP_LNKSTA);
 		speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, value);
 		width = FIELD_GET(PCI_EXP_LNKSTA_NLW, value);
 	} else {
-		value = readw(pcie->ecam + XTL_RC_PCIE_CFG_LINK_CAPS);
+		value = readl(pcie->ecam + XTL_RC_PCIE_CAP + PCI_EXP_LNKCAP);
 		speed = FIELD_GET(PCI_EXP_LNKCAP_SLS, value);
 		width = FIELD_GET(PCI_EXP_LNKCAP_MLW, value);
 	}
@@ -263,7 +262,7 @@ static bool tegra264_pcie_supports_hotplug(struct tegra264_pcie *pcie)
 static bool tegra264_pcie_link_up(struct tegra264_pcie *pcie,
 				  enum pci_bus_speed *speed)
 {
-	u16 value = readw(pcie->ecam + XTL_RC_PCIE_CFG_LINK_STATUS);
+	u16 value = readw(pcie->ecam + XTL_RC_PCIE_CAP + PCI_EXP_LNKSTA);
 
 	if (value & PCI_EXP_LNKSTA_DLLLA) {
 		if (speed)
-- 
2.53.0