Re: I915 regression : black screen at boot / Sandybridge Mobile (GT2)

On Thu, 12 Jan 2012 19:29:37 +0100
Vincent Vanackere <vincent.vanackere <at> gmail.com> wrote:

> Hi,
> 
> I when trying to run any recent (>= 3.2) kernel on my laptop (a Thinkpad
> L520), I get a black screen at boot and the screen stays black (the rest of
> the system seems fine and e.g. I can log from ssh).
> This is a regression since kernel 3.1 was working fine... I just bisected
> the problem and if I did no mistake the misbehavior was caused by the
> following commit :
> 
> ----------------------------------
> 4b645f14021871e06ce96c359bbdf0b48248c26e is the first bad commit
> commit 4b645f14021871e06ce96c359bbdf0b48248c26e
> Author: Jesse Barnes <jbarnes <at> virtuousgeek.org>
> Date:   Wed Oct 12 09:51:31 2011 -0700
> 
>     drm/i915: add PLL sharing support to handle 3 pipes
> 
>     Add two new fields to the intel_crtc struct for 3 pipe support: no_pll
>     and use_pll_a.  The no_pll field is only set on the 3rd pipe to indicate
>     that it doesn't have a PLL of its own and so shouldn't try to write the
>     main PLL regs.  The use_pll_a field controls which PLL pipe 3 will
>     share, A or B.  The core code will try to share PLLs with whichever pipe
>     has the same timings, rejecting the mode set if none is found.  This
>     means that pipe 3 must always be set after one of the other pipes has
>     been configured with real PLL settings.
> 
>     Signed-off-by: Jesse Barnes <jbarnes <at> virtuousgeek.org>