[v2,1/2] drm/msm/dpu1: don't choke on disabling the writeback connector

[György Kurucz]

Dear Leonard,

I installed KDE. First, I ran it with the my regular kernel without this 
patch. The first interesting thing I notice is that the screen *does* 
come back after resume. (The error messages are still present though.)

> Ack. Do you mean that Rob Clark also uses Yoga Slim 7x but does not face the "screen never comes back (always have to switch VT back-and-forth to bring it back)" issue?

Yes, at least that's what I gathered from our conversations on IRC. But 
with the above in mind, I now suspect that this comes down to desktop 
environment differences.

> It would be great if you can validate whether this patch breaks CRTC state (which includes the CTM state) on Yoga Slim 7x, or whether that is specific to the trogdor lazor (Chromebook Acer Spin 513), though it may require you to install KDE.

Well "Night Light" seems to be even more broken under KDE. I went into 
System Settings, set it to "Always on night light", and tried to adjust 
the temperature slider. While adjusting the slider, the screen goes 
black, and only comes back after a few seconds. The color temperature 
does not change, no matter what I change the slider to. Afterwards I 
tried with this patch as well, but it produces the exact same behavior.

Best regards,
György