[PATCH net] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

[Sean Anderson]

If coalesce_count is greater than 255 it will not fit in the register and
will overflow. Clamp it to 255 for more-predictable results.

Signed-off-by: Sean Anderson <sean.anderson at linux.dev>
Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
---

 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 9aeb7b9f3ae4..5f27fc1c4375 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -252,7 +252,8 @@ static u32 axienet_usec_to_timer(struct axienet_local *lp, u32 coalesce_usec)
 static void axienet_dma_start(struct axienet_local *lp)
 {
 	/* Start updating the Rx channel control register */
-	lp->rx_dma_cr = (lp->coalesce_count_rx << XAXIDMA_COALESCE_SHIFT) |
+	lp->rx_dma_cr = (min(lp->coalesce_count_rx, 255) <<
+			 XAXIDMA_COALESCE_SHIFT) |
 			XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_ERROR_MASK;
 	/* Only set interrupt delay timer if not generating an interrupt on
 	 * the first RX packet. Otherwise leave at 0 to disable delay interrupt.
@@ -264,7 +265,8 @@ static void axienet_dma_start(struct axienet_local *lp)
 	axienet_dma_out32(lp, XAXIDMA_RX_CR_OFFSET, lp->rx_dma_cr);
 
 	/* Start updating the Tx channel control register */
-	lp->tx_dma_cr = (lp->coalesce_count_tx << XAXIDMA_COALESCE_SHIFT) |
+	lp->tx_dma_cr = (min(lp->coalesce_count_tx, 255) <<
+			 XAXIDMA_COALESCE_SHIFT) |
 			XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_ERROR_MASK;
 	/* Only set interrupt delay timer if not generating an interrupt on
 	 * the first TX packet. Otherwise leave at 0 to disable delay interrupt.
-- 
2.35.1.1320.gc452695387.dirty