linux-kernel - Re: [PATCH 4/6] regmap: Add the LZO cache support

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Message-ID: <20110915093538.GA8631@opensource.wolfsonmicro.com>
Date:	Thu, 15 Sep 2011 10:35:38 +0100
From:	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>,
	Graeme Gregory <gg@...mlogic.co.uk>,
	Samuel Oritz <sameo@...ux.intel.com>
Subject: Re: [PATCH 4/6] regmap: Add the LZO cache support

On Mon, Sep 05, 2011 at 06:18:30PM +0200, Lars-Peter Clausen wrote:
> On 09/05/2011 03:51 PM, Dimitris Papastamos wrote:
> > This patch adds support for LZO compression when storing the register
> > cache.
> > 
> > For a typical device whose register map would normally occupy 25kB or 50kB
> > by using the LZO compression technique, one can get down to ~5-7kB.  There
> > might be a performance penalty associated with each individual read/write
> > due to decompressing/compressing the underlying cache, however that should not
> > be noticeable.  These memory benefits depend on whether the target architecture
> > can get rid of the memory occupied by the original register defaults cache
> > which is marked as __devinitconst.  Nevertheless there will be some memory
> > gain even if the target architecture can't get rid of the original register
> > map, this should be around ~30-32kB instead of 50kB.
> > 
> > Signed-off-by: Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
> > ---
> >  drivers/base/regmap/Makefile       |    2 +-
> >  drivers/base/regmap/internal.h     |    2 +
> >  drivers/base/regmap/regcache-lzo.c |  361 ++++++++++++++++++++++++++++++++++++
> >  drivers/base/regmap/regcache.c     |    1 +
> >  include/linux/regmap.h             |    1 +
> >  5 files changed, 366 insertions(+), 1 deletions(-)
> >  create mode 100644 drivers/base/regmap/regcache-lzo.c
> > 
> 
> Fails to compile due to CONFIG_LZO_{COMPRESS,DECOMPRESS} not being selected.
> Also it will have issues, with caches where we don't use raw cache defaults.

Yes, the LZO code will need to use cache_defaults instead of
cache_defaults_raw.  Since there are no users at the moment and since
most of the potential users do actually use cache_defaults_raw, I think
I can fix this incrementally.

Thanks,
Dimitris
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