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

Bjorn,

On 4/12/2017 3:19 PM, Rajat Jain wrote:

On Fri, Apr 7, 2017 at 9:55 PM, Sinan Kaya [off-list ref] wrote:

quoted

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.