[Bug 76554] [gm45 regression] [drm:init_ring_common]: *ERROR* render ring initialization failed

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76554

--- Comment #51 from Jiri Kosina <jikos at jikos.cz> ---
(In reply to comment #50)

I probably wasn't super clear what I was referring to by this comment:

> The problematic condition causing the whole ring to be claimed dead is
> 
>      I915_READ_HEAD(ring) & HEAD_ADDR) == 8
> 
> right?
> 
> I915_READ_HEAD(ring) returns 000e200c HEAD_ADDR is 0x001FFFFC, so the result
> is e200c, not the expected value of 8, causing the ring initialization
> failure.

I was referring to this:


(In reply to comment #49)
> So it passes the immediate check that HEAD is valid after setting CTRL, but
> then fails shortly afterwards. Humph. I am not sure what is going on!

because I don't see any check for HEAD validity after settin CTRL; I only see

     I915_READ_START(ring) != i915_gem_obj_ggtt_offset(obj)

check, but no I915_READ_HEAD() check ... but obviously, I am absolutely
unfamiliar with this code, so sorry for creating unnecessary noise likely.
> 
> I wonder if it is as simple as the combination of reads failing?

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