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

Manikanta Maddireddy
2026-04-10T07:39:11Z

On 10/04/26 12:10 am, Bjorn Helgaas wrote:
> On Thu, Apr 09, 2026 at 11:26:15AM +0530, Manikanta Maddireddy wrote:
>> 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
>> ...
>
>> 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.
>
> I dropped the original patch so we can just add the fixed version so
> we don't have this commit plus another commit to fix the issue.

Hi Bjorn,

I published new patch with the fix.

https://patchwork.kernel.org/project/linux-pci/patch/20260410073330.837238-1-mmaddireddy@nvidia.com/

>
>> 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.
>
> Sure. This is an x86_64 Unbuntu 25.10 system with gcc version 15.2.0
> (Ubuntu 15.2.0-4ubuntu4). Command was just "make". Config attached.
>
> Bjorn

Thank you.

I am able reproduce the error when I compiled for x86 with the attached
config.

--
nvpublic