Re: [PATCH v6 2/3] OPP: Add support for bandwidth OPP tables

[Viresh Kumar]

On 09-01-20, 10:35, Saravana Kannan wrote:
> Agreed for the example you are giving where PM domains/voltages are
> dropped automatically when dropping the device freq to suspend freq.
> I'm just wondering about a different scenario where if some power
> domain needed to be at say 0.5v when it's suspended (no consumer using
> it)

The domain should be powered off in this case I think.

> to not lose state, or to come back up without brownouts, etc then
> suspend OPP for PM domains might be useful. But I don't know enough
> about that to speak with authority, so I'll leave it at this.
> 
> I see this suspend-opp as a way to mark to what level the bandwidth
> needs to be dropped to/brought back up from during suspend/resume by
> the driver making interconnect bandwidth requests. For example, what
> if the CPU -> DDR needed to be at some level to avoid suspend/resume
> issues (say CPU bug with respect to timing/latencies)? In this
> example, the CPU driver would be the one making bandwidth requests for
> CPU -> DDR bandwidth during normal operation and during
> suspend/resume. So it's basically exactly the same way it would treat
> CPU freq OPP.

I understand your concerns but to me it all looks hypothetical right
now. I am not saying we won't support suspend-opp for interconnect or
domains, but that we should do it only if it is required.

> Btw, I don't have a strong opinion on this. But, even if we do only a
> rate comparison, what does it even mean to compare rates for genpd or
> BW opp tables?

We will never do the comparison because those tables will never have
the suspend OPP in the respective tables.

-- 
viresh