[PATCH v8 1/9] PCI: tegra194: Drive CLKREQ# signal low explicitly

Manikanta Maddireddy
2026-03-24T19:10:55Z

From: Vidya Sagar <vidyas@nvidia.com>

The Root Port's CLKREQ# signal is shared with a downstream PCIe switch and
the endpoints behind it. By default, APPL_PINMUX_CLKREQ_OVERRIDE only
overrides the CLKREQ# input to the controller (so REFCLK is enabled
internally); it does not drive the CLKREQ# output pin low. Some PCIe
switches (e.g. Broadcom PCIe Gen4) forward the Root Port's CLKREQ# to their
downstream side and expect it to be driven low for REFCLK, even when the
switch does not support CLK-PM or ASPM-L1SS. Without driving the output
pin low, link-up can fail between the switch and endpoints.

Clear APPL_PINMUX_CLKREQ_DEFAULT_VALUE so the CLKREQ# output pad is
explicitly driven low. That makes the shared CLKREQ# line low on the wire
and avoids link-up issues with such switches.

Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
---
Changes V6 -> V8: Fix commit message
Changes V1 -> V6: None

drivers/pci/controller/dwc/pcie-tegra194.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
index b497b178bb7e..c823285368f5 100644
--- a/drivers/pci/controller/dwc/pcie-tegra194.c
+++ b/drivers/pci/controller/dwc/pcie-tegra194.c
@@ -44,6 +44,7 @@
#define APPL_PINMUX_CLKREQ_OVERRIDE BIT(3)
#define APPL_PINMUX_CLK_OUTPUT_IN_OVERRIDE_EN BIT(4)
#define APPL_PINMUX_CLK_OUTPUT_IN_OVERRIDE BIT(5)
+#define APPL_PINMUX_CLKREQ_DEFAULT_VALUE BIT(13)

#define APPL_CTRL 0x4
#define APPL_CTRL_SYS_PRE_DET_STATE BIT(6)
@@ -1428,6 +1429,7 @@ static int tegra_pcie_config_controller(struct tegra_pcie_dw *pcie,
val = appl_readl(pcie, APPL_PINMUX);
val |= APPL_PINMUX_CLKREQ_OVERRIDE_EN;
val &= ~APPL_PINMUX_CLKREQ_OVERRIDE;
+ val &= ~APPL_PINMUX_CLKREQ_DEFAULT_VALUE;
appl_writel(pcie, val, APPL_PINMUX);
}

--
2.34.1