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

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Date:   Tue, 8 Dec 2020 18:18:30 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>, bhelgaas@...gle.com
Cc:     "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

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.

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