linux-kernel - Re: [PATCH RFC] eeprom: at24: extend driver to plug into the NVMEM framework

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Message-ID: <20150816131130.GC10094@lunn.ch>
Date:	Sun, 16 Aug 2015 15:11:30 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Stefan Wahren <stefan.wahren@...e.com>
Cc:	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	wsa@...-dreams.de, srinivas.kandagatla@...aro.org
Subject: Re: [PATCH RFC] eeprom: at24: extend driver to plug into the NVMEM
 framework

On Sun, Aug 16, 2015 at 10:28:06AM +0200, Stefan Wahren wrote:
> Hi Andrew,
> 
> > Andrew Lunn <andrew@...n.ch> hat am 16. August 2015 um 04:54 geschrieben:
> >
> >
> > Add a read only regmap for accessing the EEPROM, and then use that
> > with the NVMEM framework.
> >
> > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > ---
> > drivers/misc/eeprom/at24.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 65 insertions(+)
> >
> > diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> > index 2d3db81be099..0e80c0c09d4e 100644
> > --- a/drivers/misc/eeprom/at24.c
> > +++ b/drivers/misc/eeprom/at24.c
> > @@ -22,6 +22,8 @@
> > #include <linux/jiffies.h>
> > #include <linux/of.h>
> > #include <linux/i2c.h>
> > +#include <linux/nvmem-provider.h>
> > +#include <linux/regmap.h>
> 
> shouldn't the dependancies in Kconfig updated (depends on REGMAP) too?

Hi Stefan

This is why the patch is RFC.

REGMAP has stub implementations for when it is not. NVMEM also has
stub implementations. NVMEM does however select REGMAP. So it should
be possible to compile this driver without NVMEM support. Hopefully
0day will find my git branch and compile it in different ways to see
if i've got this right.

As part of RFC, is this O.K?

Another question which spring to mind is, do we want the eeprom to be
in /sys twice, the old and the new way? Backwards compatibility says
the old must stay. Do we want a way to suppress the new? Or should we
be going as far as refractoring the code into a core library, and two
wrapper drivers, old and new?

> > +static int at24_regmap_write(void *context, const void *data, size_t count)
> > +{
> > + struct at24_data *at24 = context;
> > +
> > + return at24_write(at24, data, 0, count);
> 
> Since the patch only provides read only support this function could return 0.

Humm, the comment is out of date. Regmap does not work too well
without a write method. So i ended up implementing it. But it has
hardly been tested, where as i have hammered on read.

Thanks
	Andrew
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