Bug 31311

Summary: i915.powersave option is not respected in 2.6.36
Product: DRI Reporter: Fernando Lemos <fernandotcl>
Component: DRM/IntelAssignee: Chris Wilson <chris>
Status: CLOSED FIXED QA Contact:
Severity: normal    
Priority: medium CC: jbarnes
Version: unspecified   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:

Description Fernando Lemos 2010-11-01 20:04:09 UTC 
Hi,

As reported downstream in the Debian BTS here:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=602009

Setting i915.powersave=0 no longer works. The following sequence of commands demonstrates the issue:

fernando@vostro:~$ uname -a
Linux vostro 2.6.36-trunk-amd64 #1 SMP Wed Oct 27 14:28:29 UTC 2010 x86_64 GNU/Linux
fernando@vostro:~$ sudo cat /sys/module/i915/parameters/powersave 
1
fernando@vostro:~$ grep i915 /etc/modprobe.d/*
/etc/modprobe.d/i915-kms.conf:options i915 modeset=1
/etc/modprobe.d/local.conf:options i915 powersave=0
fernando@vostro:~$ 

The exact same setup works fine in 2.6.32, 2.6.34 and 2.6.35:

fernando@vostro:~$ uname -a
Linux vostro 2.6.35-trunk-amd64 #1 SMP Tue Aug 3 21:31:37 UTC 2010 x86_64 GNU/Linux
fernando@vostro:~$ sudo cat /sys/module/i915/parameters/powersave 
0
fernando@vostro:~$ grep i915 /etc/modprobe.d/*
/etc/modprobe.d/i915-kms.conf:options i915 modeset=1
/etc/modprobe.d/local.conf:options i915 powersave=0
fernando@vostro:~$ 

I set the severity to normal instead of minor because this is the only known workaround for the following bug, as far as I can tell:

http://bugs.freedesktop.org/show_bug.cgi?id=27589

Please let me know of any information I can provide to make troubleshooting this issue easier.

Thanks in advance,
Comment 1 Chris Wilson 2010-11-02 02:27:18 UTC 
Technically this is a bug in modprobe not collating all module options at load time. i915_powersave was only ever read-only at runtime; 2.6.36 appears to be stricter in this regard and upsets your configuration.

You can either fix modprobe, manually merge the module options in i915-kms.conf + local.conf, or apply this patch from -fixes:

commit 0aa992777270f0ea7097170fa50a1d98615eb0d4
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Nov 2 09:20:50 2010 +0000

    drm/i915: Allow powersave modparam to be adjusted at runtime.
    
    2.6.36 appears to respect the 0400 mode we assigned to the parameter
    preventing it from being adjusted after loading. However, this is safe
    to adjust at runtime.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=31311
    Reported-by: Fernando Lemos <fernandotcl@gmail.com>
    Cc: stable@kernel.org
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

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