[openwrt/openwrt] realtek: RTL93xx: Make use of correct ring size counters

[LEDE Commits]

robimarko pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/a93e7251402b8599490250ea3818c27bf4184e1b

commit a93e7251402b8599490250ea3818c27bf4184e1b
Author: Markus Stockhausen <markus.stockhausen at gmx.de>
AuthorDate: Fri Sep 5 02:31:53 2025 -0400

    realtek: RTL93xx: Make use of correct ring size counters
    
    The receive path of the RTL93xx SoCs is currently discarding packets
    in software. Analysis gives the following explanation:
    
    - RX ring size registers are setup with the full software ring size
    - When packets are received the packet counter registers are increased
    - After RX processing the counter registers are changed the wrong way
    - From then SOC is allowed to receive more packets than software allows
    - Overflow interrupts are fired
    - As a reaction to that the software drops packets
    
    Change the processing as follows:
    
    - Setup ring size registers with a headroom of 2 buffers
    - Decrease the counter registers with the real work done
    
    With this change no more overflow interrupts occur because the SoC
    disables the queues before they can overflow or hit a buffer that is
    still owned by the CPU.
    
    Benchmark from single stream iperf3 run, with server process running
    on ZyXEL XGS1210 (RTL930x).
    
    iperf3 run before
    
    -----------------------------------------------------------
    Server listening on 5201 (test #1)
    -----------------------------------------------------------
    Accepted connection from 192.168.2.86, port 54412
    [  5] local 192.168.2.71 port 5201 connected to 192.168.2.86 port 54418
    [ ID] Interval           Transfer     Bitrate
    [  5]   0.00-1.00   sec   384 KBytes  3.14 Mbits/sec
    [  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   2.00-3.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   3.00-4.01   sec  5.12 MBytes  42.8 Mbits/sec
    [  5]   4.01-5.00   sec  11.4 MBytes  95.8 Mbits/sec
    [  5]   5.00-6.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   6.00-7.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   8.00-9.00   sec  0.00 Bytes  0.00 bits/sec
    [  5]   9.00-10.00  sec  0.00 Bytes  0.00 bits/sec
    
    iperf3 run after
    
    -----------------------------------------------------------
    Server listening on 5201 (test #1)
    -----------------------------------------------------------
    Accepted connection from 192.168.2.86, port 55228
    [  5] local 192.168.2.71 port 5201 connected to 192.168.2.86 port 55232
    [ ID] Interval           Transfer     Bitrate
    [  5]   0.00-1.00   sec  22.8 MBytes   191 Mbits/sec
    [  5]   1.00-2.01   sec  25.4 MBytes   211 Mbits/sec
    [  5]   2.01-3.00   sec  25.4 MBytes   215 Mbits/sec
    [  5]   3.00-4.01   sec  26.5 MBytes   220 Mbits/sec
    [  5]   4.01-5.00   sec  26.2 MBytes   222 Mbits/sec
    [  5]   5.00-6.00   sec  26.9 MBytes   225 Mbits/sec
    [  5]   6.00-7.00   sec  27.0 MBytes   226 Mbits/sec
    [  5]   7.00-8.01   sec  26.9 MBytes   224 Mbits/sec
    [  5]   8.01-9.00   sec  26.5 MBytes   223 Mbits/sec
    [  5]   9.00-10.00  sec  26.8 MBytes   225 Mbits/sec
    [  5]  10.00-10.02  sec   640 KBytes   224 Mbits/sec
    
    Signed-off-by: Markus Stockhausen <markus.stockhausen at gmx.de>
    Link: https://github.com/openwrt/openwrt/pull/19960
    Signed-off-by: Robert Marko <robimarko at gmail.com>
---
 .../files-6.12/drivers/net/ethernet/rtl838x_eth.c    | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c b/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
index 44f0fe5357..8b30ebcd85 100644
--- a/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
+++ b/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
@@ -240,25 +240,18 @@ static void rtl839x_update_cntr(int r, int released)
 
 static void rtl930x_update_cntr(int r, int released)
 {
+	u32 reg = rtl930x_dma_if_rx_ring_cntr(r);
 	int pos = (r % 3) * 10;
-	u32 reg = RTL930X_DMA_IF_RX_RING_CNTR + ((r / 3) << 2);
-	u32 v = sw_r32(reg);
 
-	v = (v >> pos) & 0x3ff;
-	pr_debug("RX: Work done %d, old value: %d, pos %d, reg %04x\n", released, v, pos, reg);
-	sw_w32_mask(0x3ff << pos, released << pos, reg);
-	sw_w32(v, reg);
+	sw_w32(released << pos, reg);
 }
 
 static void rtl931x_update_cntr(int r, int released)
 {
+	u32 reg = rtl931x_dma_if_rx_ring_cntr(r);
 	int pos = (r % 3) * 10;
-	u32 reg = RTL931X_DMA_IF_RX_RING_CNTR + ((r / 3) << 2);
-	u32 v = sw_r32(reg);
 
-	v = (v >> pos) & 0x3ff;
-	sw_w32_mask(0x3ff << pos, released << pos, reg);
-	sw_w32(v, reg);
+	sw_w32(released << pos, reg);
 }
 
 struct dsa_tag {
@@ -766,10 +759,11 @@ static void rtl93xx_hw_en_rxtx(struct rtl838x_eth_priv *priv)
 	sw_w32((DEFAULT_MTU << 16) | RX_TRUNCATE_EN_93XX, priv->r->dma_if_ctrl);
 
 	for (int i = 0; i < priv->rxrings; i++) {
+		int cnt = min(priv->rxringlen - 2, 0x3ff);
 		int pos = (i % 3) * 10;
 		u32 v;
 
-		sw_w32_mask(0x3ff << pos, priv->rxringlen << pos, priv->r->dma_if_rx_ring_size(i));
+		sw_w32_mask(0x3ff << pos, cnt << pos, priv->r->dma_if_rx_ring_size(i));
 
 		/* Some SoCs have issues with missing underflow protection */
 		v = (sw_r32(priv->r->dma_if_rx_ring_cntr(i)) >> pos) & 0x3ff;
@@ -1329,7 +1323,7 @@ static int rtl838x_hw_receive(struct net_device *dev, int r, int budget)
 	netif_receive_skb_list(&rx_list);
 
 	/* Update counters */
-	priv->r->update_cntr(r, 0);
+	priv->r->update_cntr(r, work_done);
 
 	spin_unlock_irqrestore(&priv->lock, flags);