linux-kernel - /sys/module/pcie_aspm/parameters/policy not writable?

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Message-ID: <20130709012611.GA22371@amd.pavel.ucw.cz>
Date:	Tue, 9 Jul 2013 03:26:11 +0200
From:	Pavel Machek <pavel@....cz>
To:	kernel list <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>
Cc:	joe.lawrence@...atus.com, myron.stowe@...hat.com,
	bhelgaas@...gle.com
Subject: /sys/module/pcie_aspm/parameters/policy not writable?

Hi!

My thinkpad has rather high ping latencies... and perhaps it is due to
PCIE ASPM.

Its help text says:

CONFIG_PCIEASPM:

This enables OS control over PCI Express ASPM (Active State
Power Management) and Clock Power Management. ASPM supports
state L0/L0s/L1.
...
ASPM can be disabled or enabled at runtime via
/sys/module/pcie_aspm/parameters/policy

So I tried setting the parameter, but it seems to be broken :-(

root@amd:/data/pavel# cat /sys/module/pcie_aspm/parameters/policy
[default] performance powersave 
root@amd:/data/pavel# echo performance > /sys/module/pcie_aspm/parameters/policy
bash: echo: write error: Operation not permitted
root@amd:/data/pavel# echo -n performance > /sys/module/pcie_aspm/parameters/policy
bash: echo: write error: Operation not permitted
root@amd:/data/pavel# ls -al /sys/module/pcie_aspm/parameters/policy
-rw-r--r-- 1 root root 4096 Jul  9 03:16 /sys/module/pcie_aspm/parameters/policy
root@amd:/data/pavel# cat /sys/module/pcie_aspm/parameters/policy
[default] performance powersave 
root@amd:/data/pavel# echo powersave > /sys/module/pcie_aspm/parameters/policy
bash: echo: write error: Operation not permitted
root@amd:/data/pavel# echo -n powersave > /sys/module/pcie_aspm/parameters/policy
bash: echo: write error: Operation not permitted
root@amd:/data/pavel# echo -n default > /sys/module/pcie_aspm/parameters/policy
bash: echo: write error: Operation not permitted

Hmm:

CONFIG_PCIEASPM_DEFAULT=y
# CONFIG_PCIEASPM_POWERSAVE is not set                                                     
# CONFIG_PCIEASPM_PERFORMANCE is not set                                                   

Should we avoid displaying options that can't be selected?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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