linux-kernel - [PATCH V3 02/21] PCI: tegra194: Drive CLKREQ signal low explicitly

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Date:   Fri, 14 Oct 2022 00:08:35 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     <lpieralisi@...nel.org>, <robh@...nel.org>, <kw@...ux.com>,
        <bhelgaas@...gle.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <kishon@...com>, <vkoul@...nel.org>,
        <mani@...nel.org>, <Sergey.Semin@...kalelectronics.ru>,
        <ffclaire1224@...il.com>
CC:     <linux-pci@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-phy@...ts.infradead.org>,
        <kthota@...dia.com>, <mmaddireddy@...dia.com>, <vidyas@...dia.com>,
        <sagar.tv@...il.com>
Subject: [PATCH V3 02/21] PCI: tegra194: Drive CLKREQ signal low explicitly

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 endpoints 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 endpoints. 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.

Signed-off-by: Vidya Sagar <vidyas@...dia.com>
---
V3:
* Reworded the commit message

V2:
* 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 d7ab33931de4..a33c86e3de9d 100644
--- a/drivers/pci/controller/dwc/pcie-tegra194.c
+++ b/drivers/pci/controller/dwc/pcie-tegra194.c
@@ -47,6 +47,7 @@
 #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)
@@ -1510,6 +1511,7 @@ 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);
 	}

-- 
2.17.1