netdev - Re: [PATCH net-next] net: phy: Have __phy

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Date:   Thu, 11 Jan 2018 17:29:22 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, geert@...ux-m68k.org,
        niklas.cassel@...s.com
Cc:     David Miller <davem@...emloft.net>,
        Russell King <rmk+kernel@....linux.org.uk>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: Have __phy_modify return 0 on success

On 01/11/2018 12:55 PM, 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. 

phy_restore_page() does actually use the old value returned by
__phy_modify(), but treats > 0 and == 0 the same way so it is
technically used, just not as a > 0 quantity it seems.

Russell, are there out of tree call sites (e.g: in your "phy" branch)
that we are going to be breaking if we accept this change?

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: 2b74e5be17d2 ("net: phy: add phy_modify() accessor")

You would probably want to tag it with:

Fixes: fea23fb591cc ("net: phy: convert read-modify-write to phy_modify()")

as well, because that seems to be the problem Niklas and Geert encountered.

> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
> 
> Geert, Niklas
> 
> Please can you test this and let me know if it fixes the problems you
> see.
> 
>  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..36cad6b3b96d 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);
>  
> 


-- 
Florian