linux-kernel - Re: [PATCH] mtd: onenand_base: Avoid fall-through warnings

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Message-ID: <20190522233705.234d75d5@collabora.com>
Date:   Wed, 22 May 2019 23:37:05 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Kyungmin Park <kyungmin.park@...sung.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] mtd: onenand_base: Avoid fall-through warnings

On Wed, 22 May 2019 13:04:46 -0500
"Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote:

> NOTICE THAT:
> 
> "...we don't know whether we need fallthroughs or breaks there and this
> is just a change to avoid having new warnings when switching to
> -Wimplicit-fallthrough but this change might be entirely wrong."[1]
> 
> See the original thread of discussion here:
> 
> https://lore.kernel.org/patchwork/patch/1036251/
> 
> So, in preparation to enabling -Wimplicit-fallthrough, this patch silences
> the following warnings:
> 
> drivers/mtd/nand/onenand/onenand_base.c: In function ‘onenand_check_features’:
> drivers/mtd/nand/onenand/onenand_base.c:3264:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    if (ONENAND_IS_DDP(this))
>       ^
> drivers/mtd/nand/onenand/onenand_base.c:3284:2: note: here
>   case ONENAND_DEVICE_DENSITY_2Gb:
>   ^~~~
> drivers/mtd/nand/onenand/onenand_base.c:3288:17: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    this->options |= ONENAND_HAS_UNLOCK_ALL;
> drivers/mtd/nand/onenand/onenand_base.c:3290:2: note: here
>   case ONENAND_DEVICE_DENSITY_1Gb:
>   ^~~~
> 
> Warning level 3 was used: -Wimplicit-fallthrough=3
> 
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
> 
> [1] https://lore.kernel.org/lkml/20190509085318.34a9d4be@xps13/
> 
> Cc: Miquel Raynal <miquel.raynal@...tlin.com>
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/mtd/nand/onenand/onenand_base.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
> index f41d76248550..6cf4df9f8c01 100644
> --- a/drivers/mtd/nand/onenand/onenand_base.c
> +++ b/drivers/mtd/nand/onenand/onenand_base.c
> @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)
>  			if ((this->version_id & 0xf) == 0xe)
>  				this->options |= ONENAND_HAS_NOP_1;
>  		}
> +		/* Fall through - ? */

So, the only thing that you'll re-use by falling through the next case
is the '->options |= ONENAND_HAS_UNLOCK_ALL' operation. I find it easier
to follow with an explicit copy of this line + a break.

>  
>  	case ONENAND_DEVICE_DENSITY_2Gb:
>  		/* 2Gb DDP does not have 2 plane */
>  		if (!ONENAND_IS_DDP(this))
>  			this->options |= ONENAND_HAS_2PLANE;
>  		this->options |= ONENAND_HAS_UNLOCK_ALL;
> +		/* Fall through - ? */

This fall through certainly doesn't make sense, as the only thing that
might be done in the 1Gb case is conditionally adding the
HAS_UNLOCK_ALL flag, and this flag is already unconditionally set.
Please add a break here.

>  
>  	case ONENAND_DEVICE_DENSITY_1Gb:
>  		/* A-Die has all block unlock */