http://bugzilla.kernel.org/show_bug.cgi?id=6689
Summary: AGP bus mastering inhibiting CPU power saving states???
Kernel Version: 2.6.16
Status: NEW
Severity: normal
Owner: [EMAIL PROTECTED]
Submitter: [EMAIL PROTECTED]
Most recent kernel where this bug did not occur:
Distribution:
Hardware Environment: Thinkpad X31
Software Environment: Debian Unstable, Kernel 2.6.16
Problem Description:
More a question, maybe a bug:
I have noticed that loading the radeon dri module in xorg prevents the CPU from
entering C3 power saving state. I filed a bug report (see
https://bugs.freedesktop.org/show_bug.cgi?id=7119).
The developer Michel Dänzer wondered why AGP bus mastering activity at all
inhibits the entering of C3 power saving state, as the AGP aperture is mapped
uncacheable by the CPU, so the given reason for bus mastering to prevent C3
doesn't apply technically.
Any explanation for this? Is this correct this way? Or is this a bug and the CPU
should be allowed to enter C3 even with AGP bus mastering?
For me (and some other laptop users) this makes quite a big difference, as not
loading the dri module (and the CPU entering the C3 state) gives appr. 20-30 min
more battery life (2:45 instead of 2:15). But of course, to go without 3D
acceleration is not a good compromise, either...
Steps to reproduce:
Load the radeon dri driver on a Thinkpad X31 with a Radeon Mobility M6 LY (r100)
at the start of X. Then watch /proc/acpi/processor/CPU0/power (C3 not used)
Restart X but don't load dri. Watch /proc/acpi/processor/CPU0/power (C3 used)
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