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Date: Thu, 7 Jun 2018 13:59:42 +0200
From: Boris Brezillon <boris.brezillon@bootlin.com>
To: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Cc: "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
 "marek.vasut@gmail.com" <marek.vasut@gmail.com>, Poonam Aggrwal
 <poonam.aggrwal@nxp.com>, Ashish Kumar <ashish.kumar@nxp.com>, Ying Zhang
 <ying.zhang22455@nxp.com>, Alban Bedel <albeu@free.fr>, Srinivas Kandagatla
 <srinivas.kandagatla@linaro.org>
Subject: Re: Accessing mtd partitions from driver/i2c
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On Thu, 7 Jun 2018 11:50:51 +0000
Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com> wrote:

> Hi Boris,
> 
> > -----Original Message-----
> > From: Boris Brezillon [mailto:boris.brezillon@bootlin.com]
> > Sent: Wednesday, June 6, 2018 7:26 PM
> > To: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
> > Cc: linux-mtd@lists.infradead.org; marek.vasut@gmail.com; Poonam Aggrwal
> > <poonam.aggrwal@nxp.com>; Ashish Kumar <ashish.kumar@nxp.com>; Ying
> > Zhang <ying.zhang22455@nxp.com>; Alban Bedel <albeu@free.fr>; Srinivas
> > Kandagatla <srinivas.kandagatla@linaro.org>
> > Subject: Re: Accessing mtd partitions from driver/i2c
> > 
> > +Alban and Srinivas
> > 
> > On Wed, 6 Jun 2018 13:44:32 +0000
> > Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com> wrote:
> >   
> > > Dear Borris,
> > >  
> > > > -----Original Message-----
> > > > From: Boris Brezillon [mailto:boris.brezillon@bootlin.com]
> > > > Sent: Wednesday, June 6, 2018 12:53 PM
> > > > To: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
> > > > Cc: linux-mtd@lists.infradead.org; marek.vasut@gmail.com; Poonam
> > > > Aggrwal <poonam.aggrwal@nxp.com>; Ashish Kumar
> > > > <ashish.kumar@nxp.com>; Ying Zhang <ying.zhang22455@nxp.com>
> > > > Subject: Re: Accessing mtd partitions from driver/i2c
> > > >
> > > > Hi Prabhakar,
> > > >
> > > > On Wed, 6 Jun 2018 05:02:47 +0000
> > > > Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com> wrote:
> > > >  
> > > > > Hi All,
> > > > >
> > > > > We have a requirement of using(read/write) one mtd partition from
> > > > > driver/i2c.
> > > > >
> > > > > As per my googling  mtd->_read, mtd->_write APIs has not been used  
> > > > anywhere other than driver/mtd layer.
> > > >
> > > > It's used by at least one filesystem (JFFS2). And you should not
> > > > look for mtd-  
> > > > >_xxx() users but mtd_xxx() users. You should never access the mtd
> > > > >hooks  
> > > > directly but the wrappers that are exposed by the MTD API
> > > > (mtd_read(), mtd_write(), mtd_erase(), ...).
> > > >  
> > >
> > > I can find it's usage in driver/firmware/ folder. Looks like it is
> > > using nvram.
> > >  
> > > > BTW, what's your use case? If it's about reading a piece of
> > > > information from a RO partition, then the work initiated by Alban
> > > > [1] and exposing some MTD parts are NVMEM providers should be a
> > > > better match.  
> > >
> > > Currently, Linux has i2c slave framework. It is reading/writing to DDR
> > > emulated as EEPROM (drivers/i2c/i2c-slave-eeprom.c). We want something
> > > similar, where DDR will be replaced by MTD partitions for read/write.  
> > 
> > Then NVMEM is the solution you're looking for. Alban, Srinivas, can you agree
> > on something regarding the DT bindings so that we can finally get this feature
> > merged?
> >   
> 
> Patch set[1] shared by you, only supports read. 
> Can this framework also support write?

The NVMEM framework already supports write, you just need to add write
support to the nvmem -> MTD implementation.