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

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Date:	Tue, 9 Jul 2013 09:37:26 -0700
From:	Greg KH <greg@...ah.com>
To:	Pavel Machek <pavel@....cz>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	joe.lawrence@...atus.com, myron.stowe@...hat.com,
	bhelgaas@...gle.com
Subject: Re: /sys/module/pcie_aspm/parameters/policy not writable?

On Tue, Jul 09, 2013 at 11:49:06AM +0200, Pavel Machek wrote:
> On Mon 2013-07-08 21:13:21, Greg KH wrote:
> > On Tue, Jul 09, 2013 at 03:26:11AM +0200, Pavel Machek wrote:
> > > Hi!
> > > 
> > > My thinkpad has rather high ping latencies... and perhaps it is due to
> > > PCIE ASPM.
> > 
> > Why would that be the problem?  The odds that the PCIE bus is the issue
> > seems strange to me.
> 
> Aha: I guess that's why the file is not writable:
> 
> pavel@amd:~$ dmesg | grep -i aspm 
> ACPI FADT declares the system doesn't support PCIe ASPM, so disable it
> e1000e 0000:02:00.0: Disabling ASPM L0s L1
> pavel@amd:~$ cat /sys/module/pcie_aspm/parameters/policy
> [default] performance powersave 
> pavel@amd:~$ 
> root@amd:~# echo -n performance >
> /sys/module/pcie_aspm/parameters/policy
> -su: echo: write error: Operation not permitted
> root@amd:~# 
> 
> But:
> 1) it should not list unavailable options

It's a module parameter, you can't control if they are present or not
dynamically.

> 2) operation not permitted seems like wrong error code for
> operation not supported.

Then what should it be?

greg k-h
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