ramips: add mt7621 ethernet driver improvements

- Speed up MDIO bus access
- Improve performance on tx completion

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 26 insertions, 0 deletions

diff --git a/target/linux/ramips/patches-5.4/0401-net-ethernet-mediatek-significantly-reduce-mdio-bus-.patch b/target/linux/ramips/patches-5.4/0401-net-ethernet-mediatek-significantly-reduce-mdio-bus-.patch
new file mode 100644
index 0000000000..c2ba9964e9
--- /dev/null
+++ b/target/linux/ramips/patches-5.4/0401-net-ethernet-mediatek-significantly-reduce-mdio-bus-.patch
@@ -0,0 +1,26 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 8 Jun 2020 17:02:39 +0200
+Subject: [PATCH] net: ethernet: mediatek: significantly reduce mdio bus
+ access latency
+
+usleep_range often ends up sleeping much longer than the 10-20us provided
+as a range here. This causes significant latency in mdio bus acceses,
+which easily adds multiple seconds to the boot time on MT7621 when polling
+DSA slave ports.
+Use cond_resched instead of usleep_range, since the MDIO access does not
+take much time
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
++++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+@@ -85,7 +85,7 @@ static int mtk_mdio_busy_wait(struct mtk
+ 			return 0;
+ 		if (time_after(jiffies, t_start + PHY_IAC_TIMEOUT))
+ 			break;
+-		usleep_range(10, 20);
++		cond_resched();
+ 	}
+ 
+ 	dev_err(eth->dev, "mdio: MDIO timeout\n");