linux-kernel - Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node

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Date:	Wed, 28 Oct 2015 10:14:30 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Marek Vasut <marex@...x.de>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Scott Wood <scottwood@...escale.com>,
	Josh Wu <josh.wu@...el.com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Han Xu <han.xu@...escale.com>,
	Huang Shijie <shijie.huang@....com>
Subject: Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from
 master device node

On Wed, Oct 28, 2015 at 05:32:15PM +0100, Boris Brezillon wrote:
> On Wed, 28 Oct 2015 17:11:14 +0100
> Marek Vasut <marex@...x.de> wrote:
> > On Wednesday, October 28, 2015 at 08:58:13 AM, Boris Brezillon wrote:
> > > Hi Brian,
> > 
> > Hi,
> > 
> > [...]
> > 
> > > > Are
> > > > there ever cases we want more than one (master) MTD per nand_chip? Or
> > > > vice versa?
> > > 
> > > Nope, I'd say that you always have a 1:1 relationship between a master
> > > MTD device and a NAND device.
> > 
> > Do some sorts of chipselects come into play here ? Ie. you can have one master
> > with multiple NAND chips connected to it.
> 
> Most NAND controllers support interacting with several chips (or
> dies in case your chip embeds several NAND dies), but I keep thinking
> each physical chip should have its own instance of nand_chip + mtd_info.
> If you want to have a single mtd device aggregating several chips you
> can use mtdconcat.
> 
> This leaves the multi-dies chip case, and IHMO we should represent those
> chips as a single entity, and I guess that's the purpose of the
> ->numchips field in nand_chip (if your chip embeds 2 dies with 2 CS
> lines, then ->numchips should be 2).

Yes, I think that's some of the intention there. And so even in that
case, a multi-die chip gets represented as a single struct nand_chip.

Brian
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