linux-kernel - Re: Re: [PATCH] NET/PHY: Eliminate the algorithm of forced ethernet speed reduction

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Message-ID: <1129845953.20130206091852@nita.ru>
Date:	Wed, 6 Feb 2013 09:18:52 +0000
From:	Кирилл Капранов <kkk@...a.ru>
To:	Kirill Kapranov <kapranoff@...ox.ru>
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] NET/PHY: Eliminate the algorithm of forced ethernet speed reduction


> Kirill Kapranov <kapranoff@...ox.ru> :
>> NET/PHY: Eliminate the forced speed reduction algorithm.
>> In case of the fixed speed set up for NIC 
>> (e.g. ethtool -s eth0 autoneg off speed 100 duplex full)
>> with ethernet cable plugged off, mentioned algorithm
>> slows down NIC speed, so the further "hooking up" gives
>> no result. AFAIK, this behaviour is not RFCs' recommended.
>> Tested at 2.6.38.7, applicable up to for 3.0.4. 

> (your mail user agent completely messed the patch. Please fix it.)

> I makes sense but which RFC (?) does state that said algorithm
> should not apply to the autonegotiated case as well ?

Hello, Francoi.

I am sorry for the messed letter, which I sent to You.
Please let me know, if I have to re-send my letter to mail-lists.

Now, about the criticism.

AFAIK, no one RFC describe the mentioned algorithm. I have looked up RFC-802.3, and found,
 that the mentioned algorithm is neither quoted nor described.
Thus, this algorithm is a witty invention of the developer(s), IMHO. I never observed a behaviour like this.

In the case of the autonegotiation is off and a cable plugged out, the forced slow down of the speed makes a further
 connection inoperative: a switch tries to connect with 100/full (e.g.), a NIC stays at 10/half.
So, this algorithm is destructive for the fixed speed/duplex mode.

In the auto- mode, this algorithm is inessential. The autonegotiation procedure works fine regardless an speed/duplex
 settings at the moment of connector plugging.
Because the auto mode does not need this algorithm, I dare to eliminate it at all.

--------------------------------

NET/PHY: Eliminate the forced speed reduction algorithm.
In case of the fixed speed set up for NIC 
(e.g. ethtool -s eth0 autoneg off speed 100 duplex full)
with ethernet cable plugged off, mentioned algorithm
slows down NIC speed, so the further "hooking up" gives
no result. AFAIK, this behaviour is not RFCs' recommended.
Tested at 2.6.38.7, applicable up to for 3.0.4. 
Signed-off-by: Kirill Kapranov < kkk@...a.ru >,< kapranoff@...ox.ru >
--- linux/drivers/net/phy/phy.c.orig 2011-05-22 02:13:59.000000000 +0400
+++ linux/drivers/net/phy/phy.c 2012-04-28 12:49:37.000000000 +0400
@@ -457,34 +457,6 @@ void phy_stop_machine(struct phy_device
}

/**
- * phy_force_reduction - reduce PHY speed/duplex settings by one step
- * @phydev: target phy_device struct
- *
- * Description: Reduces the speed/duplex settings by one notch,
- * in this order--
- * 1000/FULL, 1000/HALF, 100/FULL, 100/HALF, 10/FULL, 10/HALF.
- * The function bottoms out at 10/HALF.
- */
-static void phy_force_reduction(struct phy_device *phydev)
-{
- int idx;
-
- idx = phy_find_setting(phydev->speed, phydev->duplex);
- 
- idx++;
-
- idx = phy_find_valid(idx, phydev->supported);
-
- phydev->speed = settings[idx].speed;
- phydev->duplex = settings[idx].duplex;
-
- pr_info("Trying %d/%s\n", phydev->speed,
- DUPLEX_FULL == phydev->duplex ?
- "FULL" : "HALF");
-}
-
-
-/**
* phy_error - enter HALTED state for this PHY device
* @phydev: target phy_device struct
*
@@ -814,30 +786,12 @@ void phy_state_machine(struct work_struc
phydev->adjust_link(phydev->attached_dev);

} else if (0 == phydev->link_timeout--) {
- int idx;

needs_aneg = 1;
/* If we have the magic_aneg bit,
* we try again */
if (phydev->drv->flags & PHY_HAS_MAGICANEG)
break;
-
- /* The timer expired, and we still
- * don't have a setting, so we try
- * forcing it until we find one that
- * works, starting from the fastest speed,
- * and working our way down */
- idx = phy_find_valid(0, phydev->supported);
-
- phydev->speed = settings[idx].speed;
- phydev->duplex = settings[idx].duplex;
-
- phydev->autoneg = AUTONEG_DISABLE;
-
- pr_info("Trying %d/%s\n", phydev->speed,
- DUPLEX_FULL ==
- phydev->duplex ?
- "FULL" : "HALF");
}
break;
case PHY_NOLINK:
@@ -863,7 +817,6 @@ void phy_state_machine(struct work_struc
netif_carrier_on(phydev->attached_dev);
} else {
if (0 == phydev->link_timeout--) {
- phy_force_reduction(phydev);
needs_aneg = 1;
}
}

----------------------------------


--
Best regards
Kirill Kapranov


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