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

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Message-ID: <1361795118.3980.108.camel@kkk.nita.ru>
Date:	Mon, 25 Feb 2013 16:25:18 +0400
From:	Kirill Kapranov <kapranoff@...ox.ru>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] NET/PHY: Eliminate the forced speed reduction algorithm

>From Kirill Kapranov  <kkk@...a.ru>,<kapranoff@...ox.ru>

NET/PHY: Eliminate the forced speed reduction algorithm.
In case of fixed speed set up for a NIC (e.g. ethtool -s eth0 autoneg off speed 100 duplex full) with an ethernet cable plugged off, the mentioned algorithm slows down a NIC speed, so further hooking up a cable does not lead to "link" state.
Signed-off-by: Kirill Kapranov <kkk@...a.ru>,<kapranoff@...ox.ru>
---
The purpose of the introduced patch is deletion of the forced speed reduction algorithm realization from the driver module "phy".
The above mentioned algorithm works in the following way: if the PHY detected unlink line state (connector plugged off), NIC speed is decreased step-by-step in the sequence:
100 full duplex
100 half duplex
10 full duplex
10 half duplex
with the latency circa 10 s per step, and stops at 10-HD value.
I have looked up RFC-802.3, and found, that the mentioned algorithm is neither quoted nor described. AFAIK, no one RFC describe the mentioned algorithm, so it may be a witty invention of the developer(s).

In the case of the fixed speed and duplex set, with the autonegotiation off, for a NIC (e.g. # ethtool -s eth0 autoneg off speed 100 duplex full) with ethernet cable plugged off, mentioned algorithm slows down NIC speed, so when ethernet connector is plugged in, connection will be inoperative: an ethernet switch will try to connect with 100/full (e.g.), a NIC will stay at 10/half.
Thus, this algorithm is destructive for the fixed speed/duplex mode (with autonegotiation off).

In the AUTO mode, the mentioned algorithm is inessential. The autonegotiation procedure works fine regardless an speed/duplex settings at the moment of connector hooking up.
Thus, there is no point in using of this algorithm in driver.

Tested at 2.6.38.7, applicable up to for 3.0.4. 

--- 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;
 				}
 			}


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