linux-kernel - Re: [PATCH 1/8] regmap: Introduce caching support

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Message-ID: <20110902234827.GA31813@opensource.wolfsonmicro.com>
Date:	Sat, 3 Sep 2011 00:48:27 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>,
	linux-kernel@...r.kernel.org, Liam Girdwood <lrg@...com>,
	Graeme Gregory <gg@...mlogic.co.uk>,
	Samuel Oritz <sameo@...ux.intel.com>
Subject: Re: [PATCH 1/8] regmap: Introduce caching support

On Fri, Sep 02, 2011 at 10:02:02PM +0200, Lars-Peter Clausen wrote:
> On 09/02/2011 05:46 PM, Dimitris Papastamos wrote:

> > +static const struct regcache_ops *cache_types[] = {
> > +};

> I wonder if it makes sense to keep a list of regcache_ops this way, or whether
> it is not better to just pass the ops we want to use to regcache_init directly.

Or have a function per cache type.  I'm keen to hide the ops from users
because I don't want to have to worry about them peering inside the
internals.

> > +	if (!map->cache_defaults_raw || !map->num_cache_defaults_raw) {
> > +		dev_err(map->dev, "Client has not provided a defaults cache\n");
> > +		return -EINVAL;
> > +	}

> It should be OK to provide no default register values, in this case regmap
> should assume that the default for all registers is 0.

Yes - Dimitris, as we discussed offline it's pretty much essential for
things like PMICs where the defaults aren't meaningful and may even be
unknowable.

> > +			if (value && map->cache_ops->read)

> Will value or cache_ops->read ever be NULL? A register cache that either only
> provides read or write would be pretty useless in my opinion, and we should
> probably check for this at initialization time and not upon each access.

I agree that it's safe to assume read() if you've got cache_ops.  I
think in the case where we don't cache we should be able to come up with
a suitable noop cache type which we can assign as the ops so like you
say we can just assume a read() op.
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