Re: [PATCH v3 8/8] drm/etnaviv: implement per-process address spaces on MMUv2

[Philipp Zabel <p.zabel@pengutronix.de>]

On Fri, 2019-08-09 at 14:04 +0200, Lucas Stach wrote:
> This builds on top of the MMU contexts introduced earlier. Instead of having
> one context per GPU core, each GPU client receives its own context.
> 
> On MMUv1 this still means a single shared pagetable set is used by all
> clients, but on MMUv2 there is now a distinct set of pagetables for each
> client. As the command fetch is also translated via the MMU on MMUv2 the
> kernel command ringbuffer is mapped into each of the client pagetables.
> 
> As the MMU context switch is a bit of a heavy operation, due to the needed
> cache and TLB flushing, this patch implements a lazy way of switching the
> MMU context. The kernel does not have its own MMU context, but reuses the
> last client context for all of its operations. This has some visible impact,
> as the GPU can now only be started once a client has submitted some work and
> we got the client MMU context assigned. Also the MMU context has a different
> lifetime than the general client context, as the GPU might still execute the
> kernel command buffer in the context of a client even after the client has
> completed all GPU work and has been terminated. Only when the GPU is runtime
> suspended or switches to another clients MMU context is the old context
> freed up.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

regards
Philipp
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