[Bug 53926] [945gm regression] LVDS boots to blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=53926

--- Comment #43 from Nathan Schulte <nmschulte at gmail.com> ---
Created attachment 72707
  --> https://bugs.freedesktop.org/attachment.cgi?id=72707&action=edit
dmesg and intel_reg_* logs for various boots

I am experiencing this bug as well, on a fresh install of Debian Sid.  I can
control the backlight just fine, and it does indeed appear to be a race
condition as there are [rare] times that I boot into a console with KMS without
issues.

I am experiencing it with both the kernel in Debian Sid as well as the 3.7
kernel from their experimental repo:

$ uname -a # 3.2, unstable kernel
Linux desmas-l 3.2.0-4-amd64 #1 SMP Debian 3.2.35-2 x86_64 GNU/Linux

$ uname -a # 3.7, experimental kernel
Linux desmas-l 3.7-trunk-amd64 #1 SMP Debian 3.7.1-1~experimental.2 x86_64
GNU/Linux


I have found two workarounds to this:

1) Adding the i915 kernel module to my initramfs.
2) Booting with the kernel parameter video=SVIDEO-1:d


I have attached the output from dmesg for booting with the 3.2 kernel, as well
as the 3.7 kernel, all with the kernel parameter drm.debug=0xe, and for both
with and without the video=SVIDEO-1:d workaround.  In addition you will find
intel_reg_dumper outputs, as well as intel_reg_reads for 0x70000 and 0x71000
for the 3.2 boots; I could not get the tools to work for the 3.7 kernel,
failing with the following message:

Couldn't map MMIO region: Resource temporarily unavailable

Lastly, there is a dmesg from a 3.7 boot that worked without a workaround.

Please let me know if there is anything else I can assist with!  I will attempt
a git bisect as I am familiar with that process.  I can provide i915.modeset=0
or nomodeset boot dmesg logs as well if needed.

--
Nate

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