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

Manikanta Maddireddy
2026-04-09T05:56:32Z

On 09/04/26 4:00 am, Bjorn Helgaas wrote:
> 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);
> | ^~~
>

Hi Bjorn,

I don't see this error at my side, but kernel test robot reported this
error at
https://lore.kernel.org/oe-kbuild-all/202604051407.AODe3ddZ-lkp@intel.com/.

I published a patch
https://patchwork.kernel.org/project/linux-pci/patch/20260407145749.130753-1-mmaddireddy@nvidia.com/
to fix this issue.

Could you provide me your build environmental details like which tool
chain and make command are you using? I will incorporate these steps so
that I can avoid mistakes like these in future.

Thanks,
Manikanta

--
nvpublic