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Date: Thu, 31 Aug 2017 08:32:53 +0200
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Sanjay Tandel <sanjay.tandel@rockwellcollins.com>
Cc: Matt Weber <matthew.weber@rockwellcollins.com>, linux-mtd
 <linux-mtd@lists.infradead.org>, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v2] mtd: map: new driver for NXP IFC
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On Wed, 30 Aug 2017 19:03:48 -0500
Sanjay Tandel <sanjay.tandel@rockwellcollins.com> wrote:

> Hi Boris,
> 
> On Wed, Aug 30, 2017 at 2:34 PM, Boris Brezillon
> <boris.brezillon@free-electrons.com> wrote:
> > Hi,
> >
> > On Tue, 29 Aug 2017 14:47:27 -0500
> > Matt Weber <matthew.weber@rockwellcollins.com> wrote:
> >  
> >> From: Sanjay Tandel <sanjay.tandel@rockwellcollins.com>
> >>
> >> This patch adds map driver for parallel flash chips interfaced over
> >> a NXP Integrated Flash Controller (IFC). This driver allows either
> >> 8-bit or 16-bit accesses, depending on bank-width, to parallel flash
> >> chips(like Everspin MR0A16A), which are physically mapped to CPU's
> >> memory space. For unaligned accesses, it performs read-modify-write
> >> operations to keep access size same as bank-width.
> >>  
> >
> > Did you consider re-using the physmap driver [1] and adjust it to your
> > needs like the gemini [2] or versatile [3] drivers do? If you did, what
> > prevents you from using this approach?  
> 
> That approach would have coupled my driver with physmap driver, which has been
> modified in newer version of kernel. So patch would not have been backward
> compatible.

Backward compatible? I guess you meant backport-able, and I don't think
this is a good argument. We want Fixes to be backportable if they
impact several releases, not new drivers. If you want to backport your
driver to previous versions of Linux you can do it but it will never be
included in the official stable releases.

> 
> I intended to create independent driver without changing any existing
> driver code.

Please look at the versatile and gemini driver, there's almost nothing
to change in the physmap_of_core.c file, and you'll have your own
source file (+ Kconfig option) where you can tweak the map hooks as you
wish.

Regards,

Boris