[Bug 108503] Display flashes when PSR enabled on gen9

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108503

--- Comment #17 from Ronald <ronald at innovation.ch> ---
(In reply to Jose Roberto de Souza from comment #16)
> > > - can you apply this patch
> > > https://bugs.freedesktop.org/attachment.cgi?id=142181 on top of drm-tip +
> > > https://patchwork.freedesktop.org/series/50843/ and test it?(with AMD GPU
> > > still disabled)
> >Done: slightly worse than series-only, in that it appears to be harder to get the display to render (e.g. while typing in the encrypted-disk password early in >boot the display stays blank, whereas with series-only it will flash on as I type)
> 
> It fixed the blank screen when there is no updates in the screen?
No. Sorry if I wasn't clear - let me explain in more detail.

First of all, just to be clear, when I say "blank" I mean a black screen, but
backlight is still on.

Now, with just the series 50843 applied, the behaviour is that on any screen
update the display will briefly render and then go blank again shortly (on the
order of 200ms - 300ms) after the updates cease.

With the drop-frontbuffer-exits patch on top, this changes in that not all
screen updates will cause the display to be rendered, i.e. in a number of cases
the screen stays blank despite the screen having been updated. In particular
this happens (or at least is most noticeable) when the disk-password prompt is
displayed during boot: without this patch, every time a character is entered
(and hence another * is displayed in the prompt) the screen briefly renders -
with this patch the screen stays blank the whole time. Only when switching
between graphical password prompt and console (the esc key) does the screen
briefly render. This behaviour continues then through the boot animation (this
is on Fedora, where it shows an empty Fedora icon/logo that is slowly being
filled in), i.e. without the patch the logo appears (since the screen is being
constantly updated), but with the patch the screen stays blank - it's not until
we get to a late stage with the full logo present and then login manager where
the behaviour appears to then be the same as without the patch, i.e. the is
screen rendered on every update.

Hope this is clearer.

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