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

[Bjorn Helgaas <helgaas@kernel.org>]

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>
> ---
> 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);

I haven't investigated yet, but I see this build error on
pci/controller/dwc-tegra194:

    CC      drivers/pci/controller/dwc/pcie-tegra194.o
  In file included from <command-line>:
  In function ‘tegra_pcie_dw_parse_dt’,
      inlined from ‘tegra_pcie_dw_probe’ at drivers/pci/controller/dwc/pcie-tegra194.c:2148:8:
  ././include/linux/compiler_types.h:706:45: error: call to ‘__compiletime_assert_515’ declared with attribute error: min(( __builtin_constant_p(us) ? ((us) < 2 ? 0 : 63 - __builtin_clzll(us)) : (sizeof(us) <= 4) ? __ilog2_u32(us) : __ilog2_u64(us) ) + 1, 7U) signedness error
    706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	|                                             ^
  ././include/linux/compiler_types.h:687:25: note: in definition of macro ‘__compiletime_assert’
    687 |                         prefix ## suffix();                             \
	|                         ^~~~~~
  ././include/linux/compiler_types.h:706:9: note: in expansion of macro ‘_compiletime_assert’
    706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	|         ^~~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
	|                                     ^~~~~~~~~~~~~~~~~~
  ./include/linux/minmax.h:93:9: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
     93 |         BUILD_BUG_ON_MSG(!__types_ok(ux, uy),           \
	|         ^~~~~~~~~~~~~~~~
  ./include/linux/minmax.h:98:9: note: in expansion of macro ‘__careful_cmp_once’
     98 |         __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
	|         ^~~~~~~~~~~~~~~~~~
  ./include/linux/minmax.h:105:25: note: in expansion of macro ‘__careful_cmp’
    105 | #define min(x, y)       __careful_cmp(min, x, y)
	|                         ^~~~~~~~~~~~~
  drivers/pci/controller/dwc/pcie-tegra194.c:1155:43: note: in expansion of macro ‘min’
   1155 |                 pcie->aspm_l1_enter_lat = min(ilog2(us) + 1, 7U);
	|                                           ^~~