[Bug 28106] radeon KMS causes hardware conflict/interference with Intel wifi and audio, crashes wireless

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=28106

--- Comment #40 from Christian Speckner <Christian.Speckner at physik.uni-freiburg.de> 2011-05-11 13:27:56 PDT ---
Taking opportunity of the fact that this ticket is coming back to life: this
issue has still been accompanying over all mesa, X, ddx driver and kernel
updates. I'm on 2.6.38 now, and sound is still stuttering.

> Its not a fix, but a little workaround.
> open terminal
> xrandr
> look whats your minimum resolution and tha name of the screen/output
> now edit the grub linux line with video=[OUTPUTNAME]-1:[MINIMALRES]
> for me its:
> video=LVDS-1:320x200
> now reboot. KMS/VT will now have a res of 320x200, plymouth and X are normal.
> sound crickeling is gone (or I just can not notice it anymore)

I can confirm that this works for me too; I set the VT framebuffer to 640x480,
and the crackling is much better. In addition, my desktop feels significantly
faster (I'm using KDE 4.6 with kwin compositing) --- in particular, switching
desktops with many open, complex windows like firefox sitting is considerably
better now.

To the developers (and don't hesitate to beat me down if this is completely out
of question): could it be that the issue is caused by too many transfers from
system to video memory and the driver blocking interrupts while waiting for
them to complete? As I suppose that changing the framebuffer resolution affects
the VRAM layout, the impact of the above trick could be explained this way.
This could also explain the fact this issue seems to predominantly affect users
of laptops which have hardware relatively low on VRAM (64MB for my x1300
mobility). Speaking of which: the driver reports the following about my
hardware:

radeon 0000:01:00.0: VRAM: 128M 0x0000000000000000 - 0x0000000007FFFFFF (64M
used)
radeon 0000:01:00.0: GTT: 512M 0x0000000008000000 - 0x0000000027FFFFFF
[drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[drm] Driver supports precise vblank timestamp query.
radeon 0000:01:00.0: irq 49 for MSI/MSI-X
radeon 0000:01:00.0: radeon: using MSI.
[drm] radeon: irq initialized.
[drm] Detected VRAM RAM=128M, BAR=128M
[drm] RAM width 64bits DDR
[TTM] Zone  kernel: Available graphics memory: 440368 kiB.
[TTM] Zone highmem: Available graphics memory: 1295860 kiB.

I never gave it much thought, but thinking about it, this seems suspicious to
me as I am pretty sure that this device has only 64MB of VRAM.

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