[v2] net: phy: Have __phy_modify return 0 on success

__phy_modify would return the old value of the register before it was
modified. Thus on success, it does not return 0, but a positive value.
Thus functions using phy_modify, which is a wrapper around
__phy_modify, can start returning > 0 on success, rather than 0. As a
result, breakage has been noticed in various places, where 0 was
assumed.

Code inspection does not find any current location where the return of
the old value is currently used. So have __phy_modify return 0 on
success. When there is a real need for the old value, either a new
accessor can be added, or an additional parameter passed.

Fixes: fea23fb591cc ("net: phy: convert read-modify-write to phy_modify()")
Fixes: 2b74e5be17d2 ("net: phy: add phy_modify() accessor")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
v2: space before :
    additional fixes tag
    Tested-by
---
 drivers/net/phy/phy-core.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

On Fri, Jan 12, 2018 at 03:01:36PM +0100, Andrew Lunn wrote:
> __phy_modify would return the old value of the register before it was
> modified. Thus on success, it does not return 0, but a positive value.
> Thus functions using phy_modify, which is a wrapper around
> __phy_modify, can start returning > 0 on success, rather than 0. As a
> result, breakage has been noticed in various places, where 0 was
> assumed.
> 
> Code inspection does not find any current location where the return of
> the old value is currently used. So have __phy_modify return 0 on
> success. When there is a real need for the old value, either a new
> accessor can be added, or an additional parameter passed.
> 
> Fixes: fea23fb591cc ("net: phy: convert read-modify-write to phy_modify()")
> Fixes: 2b74e5be17d2 ("net: phy: add phy_modify() accessor")
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>

Hi David

Is there any particular reason you have not picked up this patch?  Do
you want more testing? An O.K. from Russell?

Thanks
	Andrew

From: Andrew Lunn <andrew@lunn.ch>
Date: Sun, 14 Jan 2018 19:04:11 +0100

> Is there any particular reason you have not picked up this patch?  Do
> you want more testing? An O.K. from Russell?

I just haven't gotten to it yet, and it's the weekend, so...

Tested-by: Niklas Cassel <niklas.cassel@axis.com>

On Fri, Jan 12, 2018 at 03:01:36PM +0100, Andrew Lunn wrote:
> __phy_modify would return the old value of the register before it was
> modified. Thus on success, it does not return 0, but a positive value.
> Thus functions using phy_modify, which is a wrapper around
> __phy_modify, can start returning > 0 on success, rather than 0. As a
> result, breakage has been noticed in various places, where 0 was
> assumed.
> 
> Code inspection does not find any current location where the return of
> the old value is currently used. So have __phy_modify return 0 on
> success. When there is a real need for the old value, either a new
> accessor can be added, or an additional parameter passed.
> 
> Fixes: fea23fb591cc ("net: phy: convert read-modify-write to phy_modify()")
> Fixes: 2b74e5be17d2 ("net: phy: add phy_modify() accessor")
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
> v2: space before :
>     additional fixes tag
>     Tested-by
> ---
>  drivers/net/phy/phy-core.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
> index e75989ce8850..4083f00c97a5 100644
> --- a/drivers/net/phy/phy-core.c
> +++ b/drivers/net/phy/phy-core.c
> @@ -336,16 +336,15 @@ EXPORT_SYMBOL(phy_write_mmd);
>   */
>  int __phy_modify(struct phy_device *phydev, u32 regnum, u16 mask, u16 set)
>  {
> -	int ret, res;
> +	int ret;
>  
>  	ret = __phy_read(phydev, regnum);
> -	if (ret >= 0) {
> -		res = __phy_write(phydev, regnum, (ret & ~mask) | set);
> -		if (res < 0)
> -			ret = res;
> -	}
> +	if (ret < 0)
> +		return ret;
>  
> -	return ret;
> +	ret = __phy_write(phydev, regnum, (ret & ~mask) | set);
> +
> +	return ret < 0 ? ret : 0;
>  }
>  EXPORT_SYMBOL_GPL(__phy_modify);
>  
> -- 
> 2.15.1
>

From: Andrew Lunn <andrew@lunn.ch>
Date: Fri, 12 Jan 2018 15:01:36 +0100

> __phy_modify would return the old value of the register before it was
> modified. Thus on success, it does not return 0, but a positive value.
> Thus functions using phy_modify, which is a wrapper around
> __phy_modify, can start returning > 0 on success, rather than 0. As a
> result, breakage has been noticed in various places, where 0 was
> assumed.
> 
> Code inspection does not find any current location where the return of
> the old value is currently used. So have __phy_modify return 0 on
> success. When there is a real need for the old value, either a new
> accessor can be added, or an additional parameter passed.
> 
> Fixes: fea23fb591cc ("net: phy: convert read-modify-write to phy_modify()")
> Fixes: 2b74e5be17d2 ("net: phy: add phy_modify() accessor")
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
> v2: space before :
>     additional fixes tag
>     Tested-by

Applied to net-next, thanks Andrew.