linux-kernel - Re: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and cmd

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Date:	Tue, 19 Jul 2016 17:59:12 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Richard Weinberger <richard@....at>
Cc:	Andrey Smirnov <andrew.smirnov@...il.com>,
	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mtd: nand: BUG_ON in case of no select_chip and
 cmd_ctrl

On Tue, 19 Jul 2016 17:44:48 +0200
Richard Weinberger <richard@....at> wrote:

> Am 19.07.2016 um 17:41 schrieb Andrey Smirnov:
> > If no user specified chip->select_chip() function is provided, code in
> > nand_base.c will automatically set this hook to nand_select_chip(),
> > which in turn depends on chip->cmd_ctrl() hook being valid. Not
> > providing both of those functions in NAND controller driver (for example
> > by mistake) will result in a bit cryptic segfault. Replace it with
> > explicit BUG_ON statement so it would be obvious what went wrong.
> > 
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> > ---
> >  drivers/mtd/nand/nand_base.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> > index ce7b2ca..57043a6 100644
> > --- a/drivers/mtd/nand/nand_base.c
> > +++ b/drivers/mtd/nand/nand_base.c
> > @@ -3128,8 +3128,10 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
> >  	if (chip->waitfunc == NULL)
> >  		chip->waitfunc = nand_wait;
> >  
> > -	if (!chip->select_chip)
> > +	if (!chip->select_chip) {
> > +		BUG_ON(!chip->cmd_ctrl);  
> 
> Please don't add new BUG_ON() calls. WARN_ON() is good enough to raise the driver developer's
> attention and won't kill the machine.

Not sure a BUG_ON() is worst than a NULL-pointer exception ;-).