Re: [PATCH v8 9/9] PCI: tegra194: Use aspm-l1-entry-delay-ns DT property for L1 entrance latency

Bjorn Helgaas
2026-04-09T18:36:40Z

On Wed, Mar 25, 2026 at 12:40:00AM +0530, Manikanta Maddireddy wrote:
> Program ASPM L1 entrance latency from the optional aspm-l1-entry-delay-ns
> device tree property instead of of_data. Convert the value from nanoseconds
> to the hardware encoding (log2(us) + 1, 3-bit field). If the property is
> absent, default to 7 (maximum latency).
>
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>

I dropped this patch from the pci/controller/dwc-tegra194 branch for
now so we could get the rest in pci/next.

> ---
> Changes V8: Use aspm-l1-entry-delay-ns instead of of_data
> Changes V1 -> V7: None
>
> drivers/pci/controller/dwc/pcie-tegra194.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 3278353b2c29..a856a48362df 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -18,6 +18,7 @@
> #include <linux/interrupt.h>
> #include <linux/iopoll.h>
> #include <linux/kernel.h>
> +#include <linux/log2.h>
> #include <linux/module.h>
> #include <linux/of.h>
> #include <linux/of_pci.h>
> @@ -272,6 +273,7 @@ struct tegra_pcie_dw {
> u32 aspm_cmrt;
> u32 aspm_pwr_on_t;
> u32 aspm_l0s_enter_lat;
> + u32 aspm_l1_enter_lat;
>
> struct regulator *pex_ctl_supply;
> struct regulator *slot_ctl_3v3;
> @@ -710,6 +712,8 @@ static void init_host_aspm(struct tegra_pcie_dw *pcie)
> val = dw_pcie_readl_dbi(pci, PCIE_PORT_AFR);
> val &= ~PORT_AFR_L0S_ENTRANCE_LAT_MASK;
> val |= (pcie->aspm_l0s_enter_lat << PORT_AFR_L0S_ENTRANCE_LAT_SHIFT);
> + val &= ~PORT_AFR_L1_ENTRANCE_LAT_MASK;
> + val |= (pcie->aspm_l1_enter_lat << PORT_AFR_L1_ENTRANCE_LAT_SHIFT);
> val |= PORT_AFR_ENTER_ASPM;
> dw_pcie_writel_dbi(pci, PCIE_PORT_AFR, val);
> }
> @@ -1110,6 +1114,7 @@ static int tegra_pcie_dw_parse_dt(struct tegra_pcie_dw *pcie)
> {
> struct platform_device *pdev = to_platform_device(pcie->dev);
> struct device_node *np = pcie->dev->of_node;
> + u32 val;
> int ret;
>
> pcie->dbi_res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dbi");
> @@ -1136,6 +1141,15 @@ static int tegra_pcie_dw_parse_dt(struct tegra_pcie_dw *pcie)
> dev_info(pcie->dev,
> "Failed to read ASPM L0s Entrance latency: %d\n", ret);
>
> + /* Default to max latency of 7. */
> + pcie->aspm_l1_enter_lat = 7;
> + ret = of_property_read_u32(np, "aspm-l1-entry-delay-ns", &val);
> + if (!ret) {
> + u32 us = max(val / 1000, 1U);
> +
> + pcie->aspm_l1_enter_lat = min(ilog2(us) + 1, 7U);
> + }
> +
> ret = of_property_read_u32(np, "num-lanes", &pcie->num_lanes);
> if (ret < 0) {
> dev_err(pcie->dev, "Failed to read num-lanes: %d\n", ret);
> --
> 2.34.1
>