[PATCH v7 1/9] PCI: tegra194: Drive CLKREQ# signal low explicitly

[Manikanta Maddireddy]

From: Vidya Sagar <vidyas@xxxxxxxxxx>

Currently, the default setting is that CLKREQ# signal of a Root Port
is internally overridden to '0' to enable REFCLK to flow out to the slot.
It is observed that one of the PCIe switches (case in point Broadcom PCIe
Gen4 switch) is propagating the CLKREQ# signal of the Root Port to the
downstream side of the switch and expecting the Endpoint devices to pull
it low so that it (PCIe switch) can give out the REFCLK although the Switch
as such doesn't support CLK-PM or ASPM-L1SS. So, as a workaround, this
patch drives the CLKREQ# of the Root Port itself low to avoid link up
issues between PCIe switch downstream port and Endpoint devices. This is
not a wrong thing to do after all the CLKREQ# is anyway being overridden
to '0' internally and now it is just that the same is being propagated
outside also.

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 -> V7: 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 b1ae46761915..2f1f882fc737 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)
@@ -1411,6 +1412,7 @@ 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