Comment # 33 on bug 68451 from Alex Deucher

(In reply to comment #27)
> fun observation:
> 
> Instead of reverting, setting this at the end of r600_cp_dma_copy_buffer()
> appears to fix it for me:
>     rctx->b.flags |= R600_CONTEXT_INV_VERTEX_CACHE;
> 
> (R600_CONTEXT_INV_CONST_CACHE will also work)
> 

Well, if we are using CP DMA to update a constant buffer or vertex buffer, we
need to flush the the apprortiate shader read caches.