Re: [PATCH v3 1/2] PCI: tegra194: Use aspm-l1-entry-delay-ns DT property for L1 entrance latency

[Bjorn Helgaas]

On Fri, May 15, 2026 at 12:37:52PM +0530, Manikanta Maddireddy wrote:
> Program the Synopsys DesignWare PORT_AFR L1 entrance latency field from the
> optional aspm-l1-entry-delay-ns device tree property (nanoseconds).
> 
> Convert delay to whole microseconds with ceiling division (DIV_ROUND_UP),
> then derive the 3-bit hw encoding as the minimum of order_base_2(us) and 7.
> If the property is not present or cannot be read, default to 7.
> 
> Hardware encoding (PORT_AFR L1 entrance latency, bits 27:29):
> 
>   +--------------------------+----------+
>   | Advertised maximum       | Code     |
>   +--------------------------+----------+
>   | Maximum of 1 us          | 000b     |
>   +--------------------------+----------+
>   | Maximum of 2 us          | 001b     |
>   +--------------------------+----------+
>   | Maximum of 4 us          | 010b     |
>   +--------------------------+----------+
>   | Maximum of 8 us          | 011b     |
>   +--------------------------+----------+
>   | Maximum of 16 us         | 100b     |
>   +--------------------------+----------+
>   | Maximum of 32 us         | 101b     |
>   +--------------------------+----------+
>   | Maximum of 64 us         | 110b     |
>   +--------------------------+----------+
>   | Rest                     | 111b     |
>   +--------------------------+----------+
> 
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
> ---
> V2: Fixed commit message as per review comments.
> V3: Fixed encoding to handle all cases per above table.
> 
>  drivers/pci/controller/dwc/pcie-tegra194.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 9dcfa194050e..5309a2f1356d 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -272,6 +272,7 @@ 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;
> @@ -715,6 +716,8 @@ 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);

Thanks for your patch!

I think follow-on patches could use FIELD_MODIFY() for
PORT_AFR_L1_ENTRANCE_LAT_MASK and PORT_AFR_L0S_ENTRANCE_LAT_MASK.

It would be good to remove all these _SHIFT #defines in a future patch,
if possible:

  PORT_AFR_L0S_ENTRANCE_LAT_SHIFT
  PORT_AFR_L1_ENTRANCE_LAT_SHIFT
  GEN3_RELATED_OFF_RATE_SHADOW_SEL_SHIFT
  PCIE_MSIX_DOORBELL_PF_SHIFT
  EVENT_COUNTER_ENABLE_SHIFT
  EVENT_COUNTER_EVENT_SEL_SHIFT
  EVENT_COUNTER_GROUP_SEL_SHIFT

The uses can probably be replaced with FIELD_MODIFY() and
FIELD_PREP(), possibly with the addition of a _MASK #define or two.

>  	val |= PORT_AFR_ENTER_ASPM;
>  	dw_pcie_writel_dbi(pci, PCIE_PORT_AFR, val);
>  }
> @@ -1115,6 +1118,7 @@ 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");
> @@ -1141,6 +1145,15 @@ 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 = DIV_ROUND_UP(val, 1000);
> +
> +		pcie->aspm_l1_enter_lat = min_t(u32, order_base_2(us), 7);
> +	}
> +
>  	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
>