linux-kernel - Re: [PATCH 5/6] mtd: rawnand: gpio: Support standard nand width

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Date:   Wed, 8 Nov 2023 16:56:59 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Aaro Koskinen <aaro.koskinen@....fi>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH 5/6] mtd: rawnand: gpio: Support standard nand width

Hi Linus,

linus.walleij@...aro.org wrote on Wed, 08 Nov 2023 15:33:53 +0100:

> The standard property for describing the band width of a NAND
> memory is "nand-bus-width" not "bank-width". The new bindings
> support both so make Linux check both in priority order.
> 
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
>  drivers/mtd/nand/raw/gpio.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/gpio.c b/drivers/mtd/nand/raw/gpio.c
> index 5553101c709c..d5bd245b0c0d 100644
> --- a/drivers/mtd/nand/raw/gpio.c
> +++ b/drivers/mtd/nand/raw/gpio.c
> @@ -183,7 +183,15 @@ static int gpio_nand_get_config(struct device *dev,
>  {
>  	u32 val;
>  
> -	if (!device_property_read_u32(dev, "bank-width", &val)) {
> +	/* The preferred binding takes precedence */
> +	if (!device_property_read_u32(dev, "nand-bus-width", &val)) {
> +		if (val == 16) {
> +			chip->options |= NAND_BUSWIDTH_16;
> +		} else if (val != 8) {
> +			dev_err(dev, "invalid nand-bus-width %u\n", val);
> +			return -EINVAL;
> +		}
> +	} else if (!device_property_read_u32(dev, "bank-width", &val)) {
>  		if (val == 2) {
>  			chip->options |= NAND_BUSWIDTH_16;
>  		} else if (val != 1) {
> 

I'm not sure this is actually needed. I believe of_get_nand_bus_width
is already called (nand_scan_ident -> rawnand_dt_init) and will set the
NAND_BUSWIDTH_16 flag automatically. So the above 'if' is already a
fallback. Maybe you can add a comment if you want to make this more
explicit that the real property is nand-bus-width and the property
parsed in the driver is for backward compatibility only?

Thanks,
Miquèl