linux-kernel - Re: [PATCH v4 28/35] mtd: rawnand: allow exiting immediately nand_scan

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Date:   Sun, 22 Jul 2018 10:49:12 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Wenyou Yang <wenyou.yang@...rochip.com>,
        Josh Wu <rainyfeeling@...look.com>,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Kamal Dasu <kdasu.kdev@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Han Xu <han.xu@....com>,
        Harvey Hunt <harveyhuntnexus@...il.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Sylvain Lemieux <slemieux.tyco@...il.com>,
        Xiaolei Li <xiaolei.li@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        Mans Rullgard <mans@...sr.com>, Stefan Agner <stefan@...er.ch>,
        linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v4 28/35] mtd: rawnand: allow exiting immediately
 nand_scan_ident()

On Fri, 20 Jul 2018 17:15:20 +0200
Miquel Raynal <miquel.raynal@...tlin.com> wrote:

> Some driver (eg. docg4) will need to handle themselves the
> identification phase. As part of the migration to use nand_scan()
> everywhere (which will unconditionnaly call nand_scan_ident()), we add
> a condition at the start of nand_scan_ident() to just "do nothing" if
> the maxchips parameters is zero, meaning that the driver does not want
> the core to handle this phase.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index dea41fa25be1..e7f135c100c2 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -5926,7 +5926,7 @@ static int nand_dt_init(struct nand_chip *chip)
>  /**
>   * nand_scan_ident - [NAND Interface] Scan for the NAND device
>   * @mtd: MTD device structure
> - * @maxchips: number of chips to scan for
> + * @maxchips: number of chips to scan for, returns immediately if 0
>   * @table: alternative NAND ID table
>   *
>   * This is the first phase of the normal nand_scan() function. It reads the
> @@ -5940,6 +5940,14 @@ int nand_scan_ident(struct mtd_info *mtd, int maxchips,
>  	struct nand_chip *chip = mtd_to_nand(mtd);
>  	int ret;
>  
> +	/*
> +	 * If the number of chips to scan for is null, just return silently.

						 ^ zero


> +	 * This is for specific drivers that must handle this part of the
> +	 * probe process themselves (e.g docg4).
> +	 */

I think that description of the special case maxchips == 0 should be
placed in the kernel doc header.

> +	if (!maxchips)
> +		return 0;

Can we move this check in nand_scan_with_ids()?

> +
>  	/* Enforce the right timings for reset/detection */
>  	onfi_fill_data_interface(chip, NAND_SDR_IFACE, 0);
>