linux-kernel - Re: [PATCH 2/2] PCI/ASPM: Use capability to override ASPM via sysfs

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Date:   Thu, 10 Dec 2020 01:50:23 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Yicong Yang <yangyicong@...ilicon.com>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] PCI/ASPM: Use capability to override ASPM via sysfs



> On Dec 9, 2020, at 01:18, Heiner Kallweit <hkallweit1@...il.com> wrote:
> 
> Am 08.12.2020 um 09:25 schrieb Kai-Heng Feng:
>> If we are to use sysfs to change ASPM settings, we may want to override
>> the default ASPM policy.
>> 
>> So use ASPM capability, instead of default policy, to be able to use all
>> possible ASPM states.
>> 
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>> ---
>> drivers/pci/pcie/aspm.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>> 
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index 2ea9fddadfad..326da7bbc84d 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -1239,8 +1239,7 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>> 
>> 		link->aspm_disable |= state;
>> 	}
>> -
>> -	pcie_config_aspm_link(link, policy_to_aspm_state(link));
>> +	pcie_config_aspm_link(link, link->aspm_capable);
>> 
> I like the idea, because the policy can be changed by the user anyway.
> Therefore I don't see it as a hard system limit.
> 
> However I think this change is not sufficient. Each call to
> pcie_config_aspm_link(link, policy_to_aspm_state(link)), e.g. in path
> pcie_aspm_pm_state_change -> pcie_config_aspm_path will reset the
> enabled states to the policy.

That's right, let me work this in v2.

Kai-Heng

> 
>> 	mutex_unlock(&aspm_lock);
>> 	up_read(&pci_bus_sem);
>> 
>