PCI: tegra: Fix PCIe host power up sequence [Linux 5.3]

This Linux kernel change "PCI: tegra: Fix PCIe host power up sequence" is included in the Linux 5.3 release. This change is authored by Manikanta Maddireddy <mmaddireddy [at] nvidia.com> on Tue Jun 18 23:31:44 2019 +0530. The commit for this change in Linux stable tree is d1f9113 (patch).

PCI: tegra: Fix PCIe host power up sequence

The PCIe host power up sequence requires to program AFI(AXI to FPCI
bridge) registers first and then PCIe registers, otherwise AFI register
settings may not latch to PCIe IP.

PCIe root port starts LTSSM as soon as PCIe xrst is deasserted.
So deassert PCIe xrst after programming PCIe registers.

Modify PCIe power up sequence as follows:

- Power ungate PCIe partition
- Enable AFI clock
- Deassert AFI reset
- Program AFI registers
- Enable PCIe clock
- Deassert PCIe reset
- Program PCIe PHY
- Program PCIe pad control registers
- Program PCIe root port registers
- Deassert PCIe xrst to start LTSSM

Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thierry Reding <treding@nvidia.com>

There are 52 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/pci/controller/pci-tegra.c | 52 ++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 22 deletions(-)

diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
index b823a63..c86e657 100644
--- a/drivers/pci/controller/pci-tegra.c
+++ b/drivers/pci/controller/pci-tegra.c
@@ -949,9 +949,6 @@ static void tegra_pcie_enable_controller(struct tegra_pcie *pcie)
        afi_writel(pcie, value, AFI_FUSE);
    }

-   /* take the PCIe interface module out of reset */
-   reset_control_deassert(pcie->pcie_xrst);
-
    /* finally enable PCIe */
    value = afi_readl(pcie, AFI_CONFIGURATION);
    value |= AFI_CONFIGURATION_EN_FPCI;
@@ -981,13 +978,11 @@ static void tegra_pcie_power_off(struct tegra_pcie *pcie)
    int err;

    reset_control_assert(pcie->afi_rst);
-   reset_control_assert(pcie->pex_rst);

    clk_disable_unprepare(pcie->pll_e);
    if (soc->has_cml_clk)
        clk_disable_unprepare(pcie->cml_clk);
    clk_disable_unprepare(pcie->afi_clk);
-   clk_disable_unprepare(pcie->pex_clk);

    if (!dev->pm_domain)
        tegra_powergate_power_off(TEGRA_POWERGATE_PCIE);
@@ -1015,25 +1010,19 @@ static int tegra_pcie_power_on(struct tegra_pcie *pcie)
    if (err < 0)
        dev_err(dev, "failed to enable regulators: %d\n", err);

-   if (dev->pm_domain) {
-       err = clk_prepare_enable(pcie->pex_clk);
+   if (!dev->pm_domain) {
+       err = tegra_powergate_power_on(TEGRA_POWERGATE_PCIE);
        if (err) {
-           dev_err(dev, "failed to enable PEX clock: %d\n", err);
+           dev_err(dev, "failed to power ungate: %d\n", err);
            goto regulator_disable;
        }
-       reset_control_deassert(pcie->pex_rst);
-   } else {
-       err = tegra_powergate_sequence_power_up(TEGRA_POWERGATE_PCIE,
-                           pcie->pex_clk,
-                           pcie->pex_rst);
+       err = tegra_powergate_remove_clamping(TEGRA_POWERGATE_PCIE);
        if (err) {
-           dev_err(dev, "powerup sequence failed: %d\n", err);
-           goto regulator_disable;
+           dev_err(dev, "failed to remove clamp: %d\n", err);
+           goto powergate;
        }
    }

-   reset_control_deassert(pcie->afi_rst);
-
    err = clk_prepare_enable(pcie->afi_clk);
    if (err < 0) {
        dev_err(dev, "failed to enable AFI clock: %d\n", err);
@@ -1054,6 +1043,8 @@ static int tegra_pcie_power_on(struct tegra_pcie *pcie)
        goto disable_cml_clk;
    }

+   reset_control_deassert(pcie->afi_rst);
+
    return 0;

 disable_cml_clk:
@@ -1062,9 +1053,6 @@ static int tegra_pcie_power_on(struct tegra_pcie *pcie)
 disable_afi_clk:
    clk_disable_unprepare(pcie->afi_clk);
 powergate:
-   reset_control_assert(pcie->afi_rst);
-   reset_control_assert(pcie->pex_rst);
-   clk_disable_unprepare(pcie->pex_clk);
    if (!dev->pm_domain)
        tegra_powergate_power_off(TEGRA_POWERGATE_PCIE);
 regulator_disable:
@@ -2130,7 +2118,12 @@ static void tegra_pcie_enable_ports(struct tegra_pcie *pcie)
             port->index, port->lanes);

        tegra_pcie_port_enable(port);
+   }

+   /* Start LTSSM from Tegra side */
+   reset_control_deassert(pcie->pcie_xrst);
+
+   list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
        if (tegra_pcie_port_check_link(port))
            continue;

@@ -2145,6 +2138,8 @@ static void tegra_pcie_disable_ports(struct tegra_pcie *pcie)
 {
    struct tegra_pcie_port *port, *tmp;

+   reset_control_assert(pcie->pcie_xrst);
+
    list_for_each_entry_safe(port, tmp, &pcie->ports, list)
        tegra_pcie_port_disable(port);
 }
@@ -2507,10 +2502,12 @@ static int __maybe_unused tegra_pcie_pm_suspend(struct device *dev)
            dev_err(dev, "failed to power off PHY(s): %d\n", err);
    }

+   reset_control_assert(pcie->pex_rst);
+   clk_disable_unprepare(pcie->pex_clk);
+
    if (IS_ENABLED(CONFIG_PCI_MSI))
        tegra_pcie_disable_msi(pcie);

-   reset_control_assert(pcie->pcie_xrst);
    tegra_pcie_power_off(pcie);

    return 0;
@@ -2532,11 +2529,19 @@ static int __maybe_unused tegra_pcie_pm_resume(struct device *dev)
    if (IS_ENABLED(CONFIG_PCI_MSI))
        tegra_pcie_enable_msi(pcie);

+   err = clk_prepare_enable(pcie->pex_clk);
+   if (err) {
+       dev_err(dev, "failed to enable PEX clock: %d\n", err);
+       goto poweroff;
+   }
+
+   reset_control_deassert(pcie->pex_rst);
+
    if (pcie->soc->program_uphy) {
        err = tegra_pcie_phy_power_on(pcie);
        if (err < 0) {
            dev_err(dev, "failed to power on PHY(s): %d\n", err);
-           goto poweroff;
+           goto disable_pex_clk;
        }
    }

@@ -2545,6 +2550,9 @@ static int __maybe_unused tegra_pcie_pm_resume(struct device *dev)

    return 0;

+disable_pex_clk:
+   reset_control_assert(pcie->pex_rst);
+   clk_disable_unprepare(pcie->pex_clk);
 poweroff:
    tegra_pcie_power_off(pcie);

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