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

[Manikanta Maddireddy]

From: Vidya Sagar <vidyas@xxxxxxxxxx>

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@xxxxxxxxxx>
Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
---
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