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

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Date:   Mon, 13 Feb 2017 11:30:24 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        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

On Fri, 10 Feb 2017 15:01:10 +0100 (CET)
Christophe Leroy <christophe.leroy@....fr> 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.

Hm, I'm not sure how this can work, because, AFAIR, the nCE line needs
to stay low for the whole CMD+ADDR[+CMD] cycle, and with your patch
it's not guaranteed.

Can you tell us more about your NAND controller?

> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  drivers/mtd/nand/gpio.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mtd/nand/gpio.c b/drivers/mtd/nand/gpio.c
> index 0d24857..85294f1 100644
> --- a/drivers/mtd/nand/gpio.c
> +++ b/drivers/mtd/nand/gpio.c
> @@ -78,7 +78,9 @@ static void gpio_nand_cmd_ctrl(struct mtd_info *mtd, int cmd, unsigned int ctrl)
>  	gpio_nand_dosync(gpiomtd);
>  
>  	if (ctrl & NAND_CTRL_CHANGE) {
> -		gpio_set_value(gpiomtd->plat.gpio_nce, !(ctrl & NAND_NCE));
> +		if (gpio_is_valid(gpiomtd->plat.gpio_nce))
> +			gpio_set_value(gpiomtd->plat.gpio_nce,
> +				       !(ctrl & NAND_NCE));
>  		gpio_set_value(gpiomtd->plat.gpio_cle, !!(ctrl & NAND_CLE));
>  		gpio_set_value(gpiomtd->plat.gpio_ale, !!(ctrl & NAND_ALE));
>  		gpio_nand_dosync(gpiomtd);
> @@ -201,7 +203,8 @@ static int gpio_nand_remove(struct platform_device *pdev)
>  
>  	if (gpio_is_valid(gpiomtd->plat.gpio_nwp))
>  		gpio_set_value(gpiomtd->plat.gpio_nwp, 0);
> -	gpio_set_value(gpiomtd->plat.gpio_nce, 1);
> +	if (gpio_is_valid(gpiomtd->plat.gpio_nce))
> +		gpio_set_value(gpiomtd->plat.gpio_nce, 1);
>  
>  	return 0;
>  }
> @@ -239,10 +242,13 @@ static int gpio_nand_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> -	ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nce, "NAND NCE");
> -	if (ret)
> -		return ret;
> -	gpio_direction_output(gpiomtd->plat.gpio_nce, 1);
> +	if (gpio_is_valid(gpiomtd->plat.gpio_nce)) {
> +		ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nce,
> +					"NAND NCE");
> +		if (ret)
> +			return ret;
> +		gpio_direction_output(gpiomtd->plat.gpio_nce, 1);
> +	}
>  
>  	if (gpio_is_valid(gpiomtd->plat.gpio_nwp)) {
>  		ret = devm_gpio_request(&pdev->dev, gpiomtd->plat.gpio_nwp,