Patch "net: dsa: microchip: use collision based back pressure mode" has been added to the 6.9-stable tree

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This is a note to let you know that I've just added the patch titled

    net: dsa: microchip: use collision based back pressure mode

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-dsa-microchip-use-collision-based-back-pressure-.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 450641787a60c2f1212b71f21ee560947fd5e40f
Author: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@xxxxxxxxxxxxxxxxxxxx>
Date:   Fri Jun 21 16:43:21 2024 +0200

    net: dsa: microchip: use collision based back pressure mode
    
    [ Upstream commit d963c95bc9840d070a788c35e41b715a648717f7 ]
    
    Errata DS80000758 states that carrier sense back pressure mode can cause
    link down issues in 100BASE-TX half duplex mode. The datasheet also
    recommends to always use the collision based back pressure mode.
    
    Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
    Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@xxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Woojung Huh <Woojung.huh@xxxxxxxxxxxxx>
    Acked-by: Arun Ramadoss <arun.ramadoss@xxxxxxxxxxxxx>
    Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index 05767d3025f77..dde5c65c2c366 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1303,6 +1303,10 @@ int ksz9477_setup(struct dsa_switch *ds)
 	/* Enable REG_SW_MTU__2 reg by setting SW_JUMBO_PACKET */
 	ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_JUMBO_PACKET, true);
 
+	/* Use collision based back pressure mode. */
+	ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_BACK_PRESSURE,
+		SW_BACK_PRESSURE_COLLISION);
+
 	/* Now we can configure default MTU value */
 	ret = regmap_update_bits(ksz_regmap_16(dev), REG_SW_MTU__2, REG_SW_MTU_MASK,
 				 VLAN_ETH_FRAME_LEN + ETH_FCS_LEN);
diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index f3a205ee483f2..fb124be8edd30 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -247,6 +247,7 @@
 #define REG_SW_MAC_CTRL_1		0x0331
 
 #define SW_BACK_PRESSURE		BIT(5)
+#define SW_BACK_PRESSURE_COLLISION	0
 #define FAIR_FLOW_CTRL			BIT(4)
 #define NO_EXC_COLLISION_DROP		BIT(3)
 #define SW_JUMBO_PACKET			BIT(2)




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