linux-kernel - RE: [PATCH V2] PCI/ASPM: reconfigure ASPM following hotplug for POLICY

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Message-ID: <92EBB4272BF81E4089A7126EC1E7B28466669BFF@IRSMSX101.ger.corp.intel.com>
Date:   Thu, 2 Mar 2017 16:05:17 +0000
From:   "Patel, Mayurkumar" <mayurkumar.patel@...el.com>
To:     'Sinan Kaya' <okaya@...eaurora.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "timur@...eaurora.org" <timur@...eaurora.org>,
        "cov@...eaurora.org" <cov@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V2] PCI/ASPM: reconfigure ASPM following hotplug for
 POLICY_DEFAULT

>
>Hi Bjorn,
>
>On 2/28/2017 1:57 PM, Patel, Mayurkumar wrote:
>>> I was trying to figure out when to use saved values vs. the values in
>>> registers by looking at the enable_cnt.
>>> enable_cnt is 0 during boot on my system.
>> enable_cnt for the root port on my system is set to 1 for "root port" already without saving
>> any ASPM related settings.
>>
>>
>
>What would be the best way to figure out when to save power-on values from
>the registers?
>

So in my case, pci_enable_device() for root port is called from pcie_port_device_register() at the boot time which
Is called from pcie_portdrv_probe() function which does not call pcie_aspm_init_link_state() but
Increment's enable_cnt field. When the Endpoint get plugged in, pcie_aspm_init_link_state() is called
from hotplug routine on "Root port" but due to enable_cnt is already incremented we do not set
right policy and aspm gets disabled by aspm driver.

Shall we introduce new atomic variable along with aspm_default in struct pci_dev and increment it in when called
first time pcie_aspm_init_link_state()  to save power-on values ( I have tested it locally, if you think could be good approach
I can upload the diffs) because enable_cnt in pci_enable_device() can be triggered
from multiple places at boot time so it might not be safe to use it? 
or adding pcie_aspm_init_link_state() in pcie_port_device_register() for ports before calling pci_enable_device()
although I am not sure whether it's the right approach and that would work for all the devices!

@Kaya/Bjorn: Do you have any other suggestions or Could you also please help by comment what would make sense?

>--
>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.
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