Re: [PATCH] video: omap2: dss: RET on idle, enable/disable dss clocks only when needed.

[Kevin Hilman <khilman@deeprootsystems.com>]

Tomi Valkeinen <tomi.valkeinen@nokia.com> writes:

> Hi,
>
> On Fri, 2009-09-18 at 19:33 +0200, ext Mike Chan wrote:
>> On Fri, Sep 18, 2009 at 1:27 AM, Tomi Valkeinen
>> <tomi.valkeinen@nokia.com> wrote:
>> > Hi,
>> >
>> > If you disable the clocks to allow RET, you also allow OFF mode. And
>> > resuming from OFF mode hasn't been implemented for DSI, if I recall
>> > right. And when I was testing it, it didn't seem to be trivial with the
>> > DSI PLL.
>> >
>> 
>> You can limiting the pwrdm next state to RET when being called from cpuidle.
>
> No, you _must_ limit it to RET. Otherwise the DSI will break down. So we
> can either keep the dsi code as it is now, or explicitely disable OFF
> mode and then apply your patch. But your patch alone won't work.

Or could add a hack to this patch so that 'enable_off_mode' doesn't
affect DSS_MOD until DSS has off-mode support.

> In the long run I think we anyway need to somehow dynamically manage the
> power state. I haven't measured it but I believe resuming from OFF will
> have a bit of a penalty, as (I think) DSI PLL etc. will have to
> reinitialized. But it would still be good to allow RET whenever
> possible, and OFF only after some period of inactivity.

This is the purpose of latency constraints.  These can be used when
the latency of going OFF will cause a problem.

Kevin