Re: [PATCH] net: 3com: 3c59x: remove set but not used variable 'mii_reg1'

[Florian Fainelli]

On 1/3/20 11:13 AM, Vladimir Oltean wrote:
> Hi Andrew,
> 
> On Fri, 3 Jan 2020 at 19:54, Andrew Lunn <andrew@xxxxxxx> wrote:
>>
>> I fully agree about the general case. However, reading the MII_BMSR
>> should not have any side affects. It would be an odd Ethernet PHY if
>> it did.
> 
> This is not really correct. As far as I know the clause 22 spec
> requires the link status bit in BMSR to be latching low, so that
> momentary losses of link can be caught post-facto.
> In fact, even genphy_update_link treats this case:
> 
>     /* The link state is latched low so that momentary link
>      * drops can be detected. Do not double-read the status
>      * in polling mode to detect such short link drops.
>      */
>     if (!phy_polling_mode(phydev)) {
>         status = phy_read(phydev, MII_BMSR);
>         if (status < 0)
>             return status;
>         else if (status & BMSR_LSTATUS)
>             goto done;
>     }
> 
> So no, reading BMSR generally is not without side effects, and that
> does not make the PHY odd.
> 
> Whether clearing the latching-low status bits is of any relevance to
> the 3com 3c59x driver bookkeeping, that I have not clue.

And since more reviewers are on the same boat, the fix should probably
look to eliminate the warning by doing something like:

(void)mdio_read(dev, vp->phys[0], MII_BMSR);
-- 
Florian