[PATCH net v2] net: xilinx: axienet: Fix IRQ coalescing packet count overflow

[Sean Anderson <sean.anderson@linux.dev>]

If coalece_count is greater than 255 it will not fit in the register and
will overflow. This can be reproduced by running

    # ethtool -C ethX rx-frames 256

which will result in a timeout of 0us instead. Fix this by clamping the
counts to the maximum value.

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

Changes in v2:
- Use FIELD_MAX to extract the max value from the mask
- Expand the commit message with an example on how to reproduce this
  issue

 drivers/net/ethernet/xilinx/xilinx_axienet.h      | 5 ++---
 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 8 ++++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet.h b/drivers/net/ethernet/xilinx/xilinx_axienet.h
index 1223fcc1a8da..54db69893565 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet.h
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet.h
@@ -109,11 +109,10 @@
 #define XAXIDMA_BD_CTRL_TXEOF_MASK	0x04000000 /* Last tx packet */
 #define XAXIDMA_BD_CTRL_ALL_MASK	0x0C000000 /* All control bits */
 
-#define XAXIDMA_DELAY_MASK		0xFF000000 /* Delay timeout counter */
-#define XAXIDMA_COALESCE_MASK		0x00FF0000 /* Coalesce counter */
+#define XAXIDMA_DELAY_MASK		((u32)0xFF000000) /* Delay timeout counter */
+#define XAXIDMA_COALESCE_MASK		((u32)0x00FF0000) /* Coalesce counter */
 
 #define XAXIDMA_DELAY_SHIFT		24
-#define XAXIDMA_COALESCE_SHIFT		16
 
 #define XAXIDMA_IRQ_IOC_MASK		0x00001000 /* Completion intr */
 #define XAXIDMA_IRQ_DELAY_MASK		0x00002000 /* Delay interrupt */
diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 9eb300fc3590..89b63695293d 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -252,7 +252,9 @@ 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 = FIELD_PREP(XAXIDMA_COALESCE_MASK,
+				   min(lp->coalesce_count_rx,
+				       FIELD_MAX(XAXIDMA_COALESCE_MASK))) |
 			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 +266,9 @@ 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 = FIELD_PREP(XAXIDMA_COALESCE_MASK,
+				   min(lp->coalesce_count_tx,
+				       FIELD_MAX(XAXIDMA_COALESCE_MASK))) |
 			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