linux-kernel - Re: [PATCH] mtd: nuc900_nand: read correct SMISR register

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Message-ID: <20160113215013.GS109450@google.com>
Date:	Wed, 13 Jan 2016 13:50:13 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Wan ZongShun <mcuos.com@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: nuc900_nand: read correct SMISR register

On Wed, Jan 13, 2016 at 10:38:08PM +0100, Arnd Bergmann wrote:
> The nuc900_nand driver has always passed an incorrect register
> address in its nuc900_check_rb() function, which cannot possibly
> work, and in some configurations gives us a build warning:
> 
> drivers/mtd/nand/nuc900_nand.c: In function 'nuc900_check_rb':
> drivers/mtd/nand/nuc900_nand.c:27:23: warning: passing argument 1 of '__raw_readl' makes pointer from integer without a cast [-Wint-conversion]
>  #define REG_SMISR     0xac
> drivers/mtd/nand/nuc900_nand.c:118:20: note: in expansion of macro 'REG_SMISR'
>   val = __raw_readl(REG_SMISR);
> 
> This makes sure we actually read from the register rather than
> from (void *)0x000000ac in user space.
> 
> I suspect nobody noticed this before because the nuc900_nand_devready()
> function never gets called, or nobody uses this driver on an upstream
> kernel. Possibly even both.

Almost definitely not the first. That's an absolutely essential
function for this driver (it doesn't have ->waitfunc(), so we use
->dev_ready() all the time). Quite likely the latter.

> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> diff --git a/drivers/mtd/nand/nuc900_nand.c b/drivers/mtd/nand/nuc900_nand.c
> index 220ddfcf29f5..dbc5b571c2bb 100644
> --- a/drivers/mtd/nand/nuc900_nand.c
> +++ b/drivers/mtd/nand/nuc900_nand.c
> @@ -113,7 +113,7 @@ static int nuc900_check_rb(struct nuc900_nand *nand)
>  {
>  	unsigned int val;
>  	spin_lock(&nand->lock);
> -	val = __raw_readl(REG_SMISR);
> +	val = __raw_readl(nand->reg + REG_SMISR);
>  	val &= READYBUSY;
>  	spin_unlock(&nand->lock);
>  

Looks OK to me, though I kinda hate dragging on support for
obviously-unused drivers...

Brian