linux-kernel - Re: [PATCH v5 13/26] memory: omap-gpmc: Support general purpose input for WAITPINs

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Message-ID: <20160307113100.2fb12bf4@bbrezillon>
Date:	Mon, 7 Mar 2016 11:31:00 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Roger Quadros <rogerq@...com>
Cc:	<tony@...mide.com>, <computersforpeace@...il.com>,
	<devicetree@...r.kernel.org>, <nsekhar@...com>,
	<linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
	<ezequiel@...guardiasur.com.ar>, <javier@...hile0.org>,
	<linux-omap@...r.kernel.org>, <dwmw2@...radead.org>,
	<fcooper@...com>
Subject: Re: [PATCH v5 13/26] memory: omap-gpmc: Support general purpose
 input for WAITPINs

On Mon, 7 Mar 2016 12:02:02 +0200
Roger Quadros <rogerq@...com> wrote:

> Hi Boris,
> 
> On 07/03/16 11:34, Boris Brezillon wrote:
> > Hi Roger,
> > 
> > On Fri, 19 Feb 2016 23:15:35 +0200
> > Roger Quadros <rogerq@...com> wrote:
> > 
> >> OMAPs can have 2 to 4 WAITPINs that can be used as general purpose
> >> input if not used for memory wait state insertion.
> >>
> >> The first user will be the OMAP NAND chip to get the NAND
> >> read/busy status using gpiolib.
> > 
> > Just a comment on this approach. Why do you need to exposed native R/B
> > pins as GPIOs? I mean, other NAND controllers are supporting R/B
> > detection using dedicated logic, and they do not exposed those pins a
> > plain GPIOs. Have you considered adding another property (rb-native ?)
> > to deal with this case instead of emulating a GPIO controller?
> > Side note: I added an rb-gpios property in my sunxi-nand DT binding
> > because in some cases, the board design forces us to use a plain GPIO.
> 
> OMAPs can have more than one WAITpins which can be used in multiple ways
> - wait state insertion
> - general purpose input
> - edge detect interrupt
> 
> It is not automatically tied to NAND read/busy# mechanism and needs software
> to get the read/busy# state.
> The register to get WAIT pin status is not situated in the NAND controller
> register space but in the parent GPMC controller space.
> 
> So we've modelled the WAIT pins as irqchip and gpiochip and users can
> use them as they want.

Okay. Thanks for the detailed explanation.

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com