linux-kernel - Re: [PATCH v3 4/9] of: mtd: add documentation for the ONFI NAND timing mode property

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Message-ID: <20140520195504.GX28907@ld-irv-0074>
Date:	Tue, 20 May 2014 12:55:04 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Rob Herring <robherring2@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Grant Likely <grant.likely@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mtd@...ts.infradead.org, dev@...ux-sunxi.org
Subject: Re: [PATCH v3 4/9] of: mtd: add documentation for the ONFI NAND
 timing mode property

On Tue, May 20, 2014 at 01:51:40PM -0600, Jason Gunthorpe wrote:
> On Tue, May 20, 2014 at 09:30:33PM +0200, Boris BREZILLON wrote:
> > AFAICT nothing, but the same goes for the ECC requirements, and we've
> > recently added DT bindings to define these requirements.
> > I'm not telling we should drop these ECC requirements bindings (actually
> > I'm using them :-)), but what's different with the timings requirements ?
> 
> ECC requirements are almost always something that has to be matched to
> the bootloader (since the bootloader typicaly reads the NAND to boot),
> so it is sensible to put that in the DT

+1 You beat me to this :)

> The timings are a property of the chip, and if they can be detected
> they should be. IMHO, the main purpose of a DT property would be to
> lower the speed if, for some reason, the board cannot support the
> device's full speed.

Agreed.

Now, we still have the open question of whether we can autodetect timing
modes easily for non-ONFI chips.

> > Indeed, I based it on the ONFI NAND timings mode model, but AFAIK
> > (tell me if I'm wrong), it should work because most of the timings
> > are min requirements.  This means, even if you provide slower
> > signals transitions, the NAND will work as expected.
> 
> IIRC for ONFI a device must always work in the mode 0 timings, without
> requiring a command?

I believe so.

FYI, despite the name of the binding, we are mostly interested in
non-ONFI NAND here.

Brian
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