linux-kernel - Re: [PATCH 7/8] drivers/i2c/busses/i2c-amd8111.c: Fix unsigned return type

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Date:	Wed, 8 Sep 2010 09:34:49 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Julia Lawall <julia@...u.dk>
Cc:	"Ben Dooks (em, bedded platforms)" <ben-linux@...ff.org>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 7/8] drivers/i2c/busses/i2c-amd8111.c: Fix unsigned
 return  type

Hi Julia,

On Wed, 8 Sep 2010 07:58:45 +0200 (CEST), Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> In each case, the function has an unsigned return type, but returns a
> negative constant to indicate an error condition.  The result of calling
> the function is always stored in a variable of type (signed) int, and thus
> unsigned can be dropped from the return type.
> 
> A sematic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @exists@
> identifier f;
> constant C;
> @@
> 
>  unsigned f(...)
>  { <+...
> *  return -C;
>  ...+> }
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  drivers/i2c/busses/i2c-amd8111.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-amd8111.c b/drivers/i2c/busses/i2c-amd8111.c
> index af1e5e2..02a3726 100644
> --- a/drivers/i2c/busses/i2c-amd8111.c
> +++ b/drivers/i2c/busses/i2c-amd8111.c
> @@ -69,7 +69,7 @@ static struct pci_driver amd8111_driver;
>   * ACPI 2.0 chapter 13 access of registers of the EC
>   */
>  
> -static unsigned int amd_ec_wait_write(struct amd_smbus *smbus)
> +static int amd_ec_wait_write(struct amd_smbus *smbus)
>  {
>  	int timeout = 500;
>  
> @@ -85,7 +85,7 @@ static unsigned int amd_ec_wait_write(struct amd_smbus *smbus)
>  	return 0;
>  }
>  
> -static unsigned int amd_ec_wait_read(struct amd_smbus *smbus)
> +static int amd_ec_wait_read(struct amd_smbus *smbus)
>  {
>  	int timeout = 500;
>  
> 

Thanks for reporting. Unfortunately the fix above is incomplete.
amd_ec_wait_write() and amd_ec_wait_read() are called by amd_ec_read()
and amd_ec_write(), which will now attempt to return negative error
codes as unsigned ints. So amd_ec_read() and amd_ec_write() must have
their return type fixed too.

Note that the driver code never checks for errors returned by
amd_ec_read() or amd_ec_write() anyway, so the fix alone is a no-op. A
real fix would have to also update the caller sites to properly deal
with errors if then happen.

-- 
Jean Delvare
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