linux-kernel - Re: [PATCH v3 1/9] mtd: nand: define struct nand

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Message-ID: <20140520181312.GR28907@ld-irv-0074>
Date:	Tue, 20 May 2014 11:13:12 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Boris BREZILLON <b.brezillon.dev@...il.com>,
	devicetree@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-doc@...r.kernel.org, dev@...ux-sunxi.org,
	linux-kernel@...r.kernel.org,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Rob Herring <robherring2@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	linux-mtd@...ts.infradead.org,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/9] mtd: nand: define struct nand_timings

On Thu, May 08, 2014 at 03:29:30PM +0100, Lee Jones wrote:
> > 
> > Please document the units for these fields here. It looks like you're
> > using picoseconds.
> 
> Can't we leave this open to interpretation?  For instance, it's more
> convenient for our driver to handle these as nano second values.

No, their values will be determined by the nand_base core, and we must
have something consistent for drivers to rely on. However, I don't
really have a hard preference on nanoseconds versus picoseconds. If we
see that many of the values reach low-digit nanosecons, or fractional
nanoseconds, it probably makes sense to have the higher resolution.

> > > +struct nand_sdr_timings {
...
> > > +	u32 tCS_min;
> 
> 	u32 tCSD_min;

Is this a suggested addition, Lee? I agree with Boris that this looks
like a DDR mode, which should not be covered here.

> > > +	u32 tDH_min;
> > > +	u32 tDS_min;
> > > +	u32 tFEAT_max;
> > > +	u32 tIR_min;
> > > +	u32 tITC_max;
> 
> 	u32 tR_max;

Same here, is this a suggested new field? If you need it, then we can
follow up like Boris suggested, with a different method, since tR is not
part of the electrical parameters of the timing mode.

...
> > > +};
> > > +
> > >  #endif /* __LINUX_MTD_NAND_H */

Brian
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