netdev - Re: [PATCH v4 3/5] net: macb: fix macb_get/set

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Message-ID: <c0bc2167-e49e-1026-94e3-cb5931755389@microchip.com>
Date:   Wed, 13 May 2020 16:16:04 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     <linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
        "Claudiu Beznea" <claudiu.beznea@...rochip.com>,
        <harini.katakam@...inx.com>,
        "Alexandre Belloni" <alexandre.belloni@...tlin.com>,
        <f.fainelli@...il.com>, <antoine.tenart@...tlin.com>,
        <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v4 3/5] net: macb: fix macb_get/set_wol() when moving to
 phylink

Russell,

Thanks for the feedback.

On 13/05/2020 at 15:05, Russell King - ARM Linux admin wrote:
> On Wed, May 06, 2020 at 01:37:39PM +0200, nicolas.ferre@...rochip.com wrote:
>> From: Nicolas Ferre <nicolas.ferre@...rochip.com>
>>
>> Keep previous function goals and integrate phylink actions to them.
>>
>> phylink_ethtool_get_wol() is not enough to figure out if Ethernet driver
>> supports Wake-on-Lan.
>> Initialization of "supported" and "wolopts" members is done in phylink
>> function, no need to keep them in calling function.
>>
>> phylink_ethtool_set_wol() return value is not enough to determine
>> if WoL is enabled for the calling Ethernet driver. Call it first
>> but don't rely on its return value as most of simple PHY drivers
>> don't implement a set_wol() function.
>>
>> Fixes: 7897b071ac3b ("net: macb: convert to phylink")
>> Signed-off-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
>> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>> Cc: Claudiu Beznea <claudiu.beznea@...rochip.com>
>> Cc: Harini Katakam <harini.katakam@...inx.com>
>> Cc: Antoine Tenart <antoine.tenart@...tlin.com>
>> ---
>>   drivers/net/ethernet/cadence/macb_main.c | 18 ++++++++++--------
>>   1 file changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
>> index 53e81ab048ae..24c044dc7fa0 100644
>> --- a/drivers/net/ethernet/cadence/macb_main.c
>> +++ b/drivers/net/ethernet/cadence/macb_main.c
>> @@ -2817,21 +2817,23 @@ static void macb_get_wol(struct net_device *netdev, struct ethtool_wolinfo *wol)
>>   {
>>        struct macb *bp = netdev_priv(netdev);
>>
>> -     wol->supported = 0;
>> -     wol->wolopts = 0;
>> -
>> -     if (bp->wol & MACB_WOL_HAS_MAGIC_PACKET)
>> +     if (bp->wol & MACB_WOL_HAS_MAGIC_PACKET) {
>>                phylink_ethtool_get_wol(bp->phylink, wol);
>> +             wol->supported |= WAKE_MAGIC;
>> +
>> +             if (bp->wol & MACB_WOL_ENABLED)
>> +                     wol->wolopts |= WAKE_MAGIC;
>> +     }
>>   }
>>
>>   static int macb_set_wol(struct net_device *netdev, struct ethtool_wolinfo *wol)
>>   {
>>        struct macb *bp = netdev_priv(netdev);
>> -     int ret;
>>
>> -     ret = phylink_ethtool_set_wol(bp->phylink, wol);
>> -     if (!ret)
>> -             return 0;
>> +     /* Pass the order to phylink layer.
>> +      * Don't test return value as set_wol() is often not supported.
>> +      */
>> +     phylink_ethtool_set_wol(bp->phylink, wol);
> 
> If this returns an error, does that mean WOL works or does it not?

In my use case (simple phy: "Micrel KSZ8081"), if I have the error 
"-EOPNOTSUPP", it simply means that this phy driver doesn't have the 
set_wol() function. But on the MAC side, I can perfectly wake-up on WoL 
event as the phy acts as a pass-through.

> Note that if set_wol() is not supported, this will return -EOPNOTSUPP.
> What about other errors?

True, I don't manage them. But for now this patch is a fix that only 
reverts to previous behavior. In other terms, it only fixes the regression.

But can I make the difference, and how, between?
1/ the phy doesn't support WoL and could prevent the WoL to happen on 
the MAC
2/ the phy doesn't implement (yet) the set_wol() function, if MAC can 
manage, it's fine


> If you want to just ignore the case where it's not supported, then
> this looks like a sledge hammer to crack a nut.

Do you suggest that I just don't call phylink_ethtool_set_wol() at all?

But what if the underlying phy does support WoL?

Best regards,
-- 
Nicolas Ferre