https://bugs.freedesktop.org/show_bug.cgi?id=91880
--- Comment #66 from Alex Deucher alexdeucher@gmail.com --- (In reply to Julian from comment #65)
(In reply to Alex Deucher from comment #64)
(In reply to Julian from comment #63)
At first I thought it was an issue with the writeback feature that caches certain register values because it also caches an rptr value that is used in the driver's gpu_lockup_check and is, to my knowledge, never actually written to.
More likely it never gets written because the GPU has hung due to something else.
Sorry, I meant that I've searched the radeon source for the lines of code where the value was accessed from. I've only found instances of it being read, no instances of it being written to. But I won't put too much stock into that since I hardly know the code base at all. I plan to mess with the code a little now that I know how to compile single modules. If I find something substantial that this might be a bug, I'll open a new issue about it.
The gpu writes to it. The driver only reads from it. The GPU shadows the value in system memory so that the driver doesn't have to read the register directly.