Re: radeon m7 hang with gears...hopefully fixed..

[Keith W. <ke...@tu...>]

Dave Airlie wrote:
>>yes, your patch fixed the glxgears-lockup for me, too. Thanks!
>>It looks like this is only necessary on RV200 based chips, maybe a comment in
>>the source about this behavior might be usefull, otherwise this workaround
>>will get removed in the future again... because other radeons work well
>>without it...
> 
> 
> If its only RV200 I'll put a check in as I think this may be an expensive
> workaround.... I'll get some more time this week to work on it, (I
> actually got paid hourly to track this down so staring at it for two
> days wasn't as bad as it could have been :-)
> 
> I'll cook up a proper patch.. Keith you know why this is needed (sounds
> like you might know why zbs should be emitted considering none of my rv200
> docs mention it) ... is it acting like a nop or does it do something ...

No, I never knew why it was necessary - presumably it is forcing a flush 
somewhere in the hardware as a sideeffect.  Zbias is a fairly unused 
piece of state so might not be pipelined to the degree of other more 
common state changes.  Possibly there's a hardware or driver bug that 
raises its head if we don't do this additional pipeline flushing.

Anyway, that's all speculation.  I found the workaround by trial and 
error and it seems to still be necessary.

Keith