[Bug 55500] [sna gen4] corrupt rendering (and flickering on redraw)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=55500

--- Comment #85 from Zdenek Kabelac <zdenek.kabelac at gmail.com> ---
(In reply to comment #84)
> Yes, that is characteristic of this bug. The internal vertex/texture
> coordinates that are being passed along the GPU pipeline become corrupt (it
> looks like we overflow a small ring buffer). The only effective approach

If it would be plain 'overflow' - than I'd be seeing this kind of corruption
always right after X starts.

But it seems like i.e. Firefox must be used for certain period of time,
to make these corruptions visible.

Surely I'm not not an expert on GPU programming - but maybe when the physical
memory gets fragmented enough after some usage there are some 'cached bo'
objects - maybe their usage is not fully synchronized?

Also the effect could also disappear (I've not yet noticed any particular way
for that) - so then Firefox scroll even the very same pages and there
is no problem (i.e. now I run still the same session - and I do not get any
visible problem)

> I've found so far has been to keep the number of rectangles inside the GPU
> pipeline below a magic value - but that is quite tricky here, and the

Well why the number would sometimes work for ours without a single visible
problem, and suddenly start to show them again?

My impression here is, when this problem is visible,
it looks like operations is working with 'wrong' parameters
(i.e. sometimes I see the image stretched, inverted, zoomed)

Maybe parameters have only some bits mangled - not fully synchronized memory
from CPU for GPU??

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