[Bug 101205] [i915][BYT] Blank screen on DSI panel

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101205

--- Comment #19 from Innocent Bystander <dimitry at cos.flag.org> ---
(In reply to Jani Nikula from comment #18)
> The VBT for the non-working Pipo X8S does not seem to have any real contents
> in the MIPI DSI sequence block, which is surprising. I can think of two
> scenarios here:
> 
> 1) You've changed the boot mode when installing. It's surprisingly common
> that the VBT is different for UEFI vs. legacy boot. Though this is usually
> more of an issue on Windows based machines, not sure about Android. (But I
> guess this is originally dual boot?)

The unit only has UEFI mode -- no legacy boot. I kept it as-is and I am booting
in UEFI using GRUB. 

It originally came with Windows and Android dual boot option.

> 2) The vendor failed to make the panel work using the VBT sequences, and
> opted to hack it all in the driver. It's usual that the vendor kernels have
> quite a bit of delta from upstream. You could try to find the sources for
> the kernels used in both devices, and compare.

I don't think that's the case. On Windows they are running Intel HD Graphics
driver.

On Android side itsa anzhen4_mrd8_w base, which I believe is a base for Intel
BayTrail-T devices. I installed a terminal app and discovered that they are
running kernel 3.10.20 and using i915 driver.

Sadly I have failed horribly trying to compile an Android kernel.

> In any case effectively reverse engineering this kind of non-standard,
> typically one-off products is not a priority in the upstream driver. If it
> works, great. If you figure out how to make it work, and contribute
> upstream, great. But we won't go out of our way to fix this.

BTW, I've had exact same phenomena with some of the Dell Venue 8 Pro tablets.
They would just go blank as soon as the i915 driver loaded. Similarly, they've
worked totally fine in Windows with Intel HD Graphics driver.

I've abandoned them in favor of these units... And now I am back to square
zero.

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