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Date: Tue, 2 May 2017 11:03:34 +0200
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Christophe LEROY <christophe.leroy@c-s.fr>
Cc: Brian Norris <computersforpeace@gmail.com>, Richard Weinberger
 <richard@nod.at>, David Woodhouse <dwmw2@infradead.org>, Marek Vasut
 <marek.vasut@gmail.com>, Cyrille Pitchen <cyrille.pitchen@atmel.com>,
 linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: nand: gpio: make nCE GPIO optional
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On Tue, 2 May 2017 07:47:40 +0200
Christophe LEROY <christophe.leroy@c-s.fr> wrote:

> Le 01/05/2017 =C3=A0 23:46, Brian Norris a =C3=A9crit :
> > On Fri, Feb 10, 2017 at 03:01:10PM +0100, Christophe Leroy wrote: =20
> >> On some hardware, the nCE signal is wired to the ChipSelect associated
> >> to bus address of the NAND, so it is automatically driven during the
> >> memory access and it is not managed by a GPIO.
> >>
> >> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> =20
> >
> > Not really a problem with this patch exactly, but FYI you're only making
> > this optional for the non-DT case. For device tree, this is kinda hard
> > to do, since the current binding suggests we retrieve the GPIOs based on
> > index position, not by name. So if you leave one off...I guess we well
> > just be off-by-1 on the indeces until we hit a non-optional one...which
> > I guess is "CLE".
> >
> > If we wanted this to work for DT, we'd need to extend this driver (and
> > binding doc) to support requesting GPIOs by name.
> > =20
>=20
> It works for me with devicetree.
>=20
> I have the following definition in my DT:
>=20
> 		nand@1,0 {
> 			compatible =3D "gpio-control-nand";
> 			reg =3D <1 0x0 0x01>;
> 			#address-cells =3D <1>;
> 			#size-cells =3D <1>;
> 			gpios =3D <&qe_pio_c 24 1 	// RDY
> 				 0			// nCE
> 				 &qe_pio_c 26 1		// ALE
> 				 &qe_pio_c 25 1		// CLE
> 				 0>;			// nwp =20
> 		};
>=20

Yep, it's perfectly fine to have 'empty' gpio entries (entries with
phandle set to 0/NULL), we're using this trick in the atmel_nand
driver as well.