Re: [PATCH 0/8] arm64: dts: qcom: Add t-power-on-us property for PCIe root ports

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 9/21/26 1:34 PM, Manivannan Sadhasivam wrote:
> On Mon, Sep 21, 2026 at 04:40:43PM +0530, Krishna Chaitanya Chundru wrote:
>>
>>
>> On 9/21/2026 2:09 PM, Konrad Dybcio wrote:
>>> On 9/11/26 8:50 AM, Krishna Chaitanya Chundru wrote:
>>>> The Qualcomm PCIe host controller driver added support for parsing the
>>>> -power-on-us property[1] from each Root Port node and programming it as
>>>> art of host initialization (PCI: qcom: Program T_POWER_ON) [2]. Prior to
>>>> this, T_POWER_ON was expected to be programmed correctly in hardware or
>>>> by the bootloader, but not all targets support this, which can lead to an
>>>> incorrectly calculated LTR_L1.2_THRESHOLD in aspm.c and improper L1.2 exit
>>>> behavior.
>>> This is a good problem description. Does it have observable effects
>>> that could also be mentioned here, beyond perhaps lspci reporting
>>> an odd value?
>> we haven't seen direct problem till now, but we might seen some issue due to
>> incorrect LTR_L1.2_THRESHOLD value.
> 
> Can you specify what issue can be seen without this series? I'd assume the
> link will fail to enter L1.2 and will result in slightly more power drain as
> the link can only enter L1.1.

Would that produce an explicit warning message somewhere?

i.e. can I reasonably be able to tell I'm missing this change and
I need it?

(if not, this is of course not a blocker, but the answer to that
question is always worth sharing)

Konrad