r8152: limit the RX buffer size of RTL8153A for USB 2.0

[ Upstream commit f91a50d8b51b5c8ef1cfb08115a005bba4250507 ]

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: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index fd5ca11c4cbb94b068d2c6153618a24bd1fe3334..390d9e1fa7fe74b3c809ad41dd12997662986139 100644 (file)
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -6502,7 +6502,10 @@ 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;