Re: [PATCH V2 1/4] regmap: cache: Add "was_reset" argument to regcache_sync_region()

From: Mark Brown
Date: Wed Apr 29 2015 - 13:34:24 EST

On Wed, Apr 29, 2015 at 10:02:03AM -0700, Kevin Cernekee wrote:
> On Wed, Apr 29, 2015 at 9:46 AM, Mark Brown <broonie@xxxxxxxxxx> wrote:

> > We just need a single boolean?

> Right, so if we add a per-regmap bool that tells us whether the device
> has been reset, then in the case of "not reset" we will have to write
> every regcache entry out to the device. Even the ones that weren't
> touched while in cache_only mode. This makes the "not reset" case
> much less efficient than the "reset" case.

The immediate point is to provide a useful external interface, the
internal optimisation is much less urgent (and it's less clear to me how
often we're going to need to do that at all - generally cache only and
power loss go together.

> BTW, any preferences on naming for the bool or for the renamed
> mark_dirty function?

Not urgently. Note that I'm *not* suggesting an immediate rename,
that's definitely a separate change (which will be a lot more painful to
merge due to cross tree issues).

> >> i.e. regcache_sync() finds a register value marked "present". How do
> >> we know whether we need to write it back to the hardware? For the
> >> special case of "cached non default register values immediately after
> >> a HW reset" you can mostly figure this out, but if there was no HW
> >> reset how do we know which entries changed while the HW was
> >> inaccessible?

> > In the first instance do we care?

> I'm not sure I understand the question.

Do we actually care about getting a list of the changed registers that

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