linux-kernel - Re: [PATCH] mtd: nand: gpio: make nCE GPIO optional

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Date:   Tue, 2 May 2017 07:47:40 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Brian Norris <computersforpeace@...il.com>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: nand: gpio: make nCE GPIO optional



Le 01/05/2017 à 23:46, Brian Norris a écrit :
> On Fri, Feb 10, 2017 at 03:01:10PM +0100, Christophe Leroy wrote:
>> 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@....fr>
>
> 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.
>

It works for me with devicetree.

I have the following definition in my DT:

		nand@1,0 {
			compatible = "gpio-control-nand";
			reg = <1 0x0 0x01>;
			#address-cells = <1>;
			#size-cells = <1>;
			gpios = <&qe_pio_c 24 1 	// RDY
				 0			// nCE
				 &qe_pio_c 26 1		// ALE
				 &qe_pio_c 25 1		// CLE
				 0>;			// nwp
		};

Christophe