Re: [PATCH V8 4/5] PCI/ASPM: save power on values during bridge init

[Sinan Kaya]

Bjorn,

On 4/12/2017 3:19 PM, Rajat Jain wrote:
> On Fri, Apr 7, 2017 at 9:55 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote:
>> Now that we added a hook to be called from device_add, save the
>> default values from the HW registers early in the boot for further
>> reuse during hot device add/remove operations.
>>
>> If the link is down during boot, assume that we want to enable L0s
>> and L1 following hotplug insertion as well as L1SS if supported.
> 
> IIUC, so far POLICY_DEFAULT meant that we'd just use & follow what
> BIOS has done, and play it safe (never try to be more opportunistic).
> With this change however, we'd be slightly overstepping and giving
> ourselves benefit of doubt if the BIOS could not enable ASPM states
> because the link was not up. This may be good, but I think we should
> call it out, and add some more elaborate comment on the POLICY_DEFAULT
> description (what to, and what not to expect in different situations).
> 
> It is important because existing systems today, that used to boot
> without cards and later hotplugged them, didn't have ASPM states
> enabled. They will now suddenly start seeing all ASPM states enabled
> including L1 substates for the first time (if supported).
> 

Rajat has a good point here. Would you like me to update the ASPM document
with this new behavior for hotplug?

Do you have another behavior preference when it comes this?

Sinan

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.