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 21:55:24 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	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>,
	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

Brian Norris <computersforpeace@...il.com> writes:

>> > 
>> > 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.

Isn't there the case of a single NAND controller with 2 identical chips, each a
8 bit NAND chip, and the controller aggregating them to offer the OS a single
16-bit NAND chip ?

In this case, the controller (pxa3xx is a good example) will be programmed to
handle both chips at the same time, and calculate CRC on both chips, etc ... I
hope the assertion "physical chip should have its own instance of nand_chip +
mtd_info" does take into account this example.

I don't know if there is actually any user of this for either pxa3xx or another
controller, nor if there is any value in this.

Cheers.

-- 
Robert
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