From f91a50d8b51b5c8ef1cfb08115a005bba4250507 Mon Sep 17 00:00:00 2001
From: Hayes Wang <hayeswang@realtek.com>
Date: Fri, 19 Mar 2021 15:37:21 +0800
Subject: [PATCH] r8152: limit the RX buffer size of RTL8153A for USB 2.0
Git-commit: f91a50d8b51b5c8ef1cfb08115a005bba4250507
References: git-fixes
Patch-mainline: v5.12-rc5

If the USB host controller is EHCI, the throughput is reduced from
300Mb/s to 60Mb/s, when the rx buffer size is modified from 16K to
32K.

According to the EHCI spec, the maximum size of the qTD is 20K.
Therefore, when the driver uses more than 20K buffer, the latency
time of EHCI would be increased. And, it let the RTL8153A get worse
throughput.

However, the driver uses alloc_pages() for rx buffer, so I limit
the rx buffer to 16K rather than 20K.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=205923
Fixes: ec5791c202ac ("r8152: separate the rx buffer size")
Reported-by: Robert Davies <robdavies1977@gmail.com>
Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/net/usb/r8152.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index 90f1c0200042..20fb5638ac65 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -6553,7 +6553,10 @@ static int rtl_ops_init(struct r8152 *tp)
 		ops->in_nway		= rtl8153_in_nway;
 		ops->hw_phy_cfg		= r8153_hw_phy_cfg;
 		ops->autosuspend_en	= rtl8153_runtime_enable;
-		tp->rx_buf_sz		= 32 * 1024;
+		if (tp->udev->speed < USB_SPEED_SUPER)
+			tp->rx_buf_sz	= 16 * 1024;
+		else
+			tp->rx_buf_sz	= 32 * 1024;
 		tp->eee_en		= true;
 		tp->eee_adv		= MDIO_EEE_1000T | MDIO_EEE_100TX;
 		break;
-- 
2.26.2