[PATCH v1 1/1] net: macb: Shorten max_tx_len to 4KiB - 56 on mpfs

[<daire.mcnamara@microchip.com>]

From: Daire McNamara <daire.mcnamara@microchip.com>

On mpfs, with SRAM configured for 4 queues, setting max_tx_len
to GEM_TX_MAX_LEN=0x3f0 results multiple AMBA errors.
Setting max_tx_len to (4KiB - 56) removes those errors.

The details are described in erratum 1686 by Cadence

The max jumbo frame size is also reduced for mpfs to (4KiB - 56).

Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
---
 drivers/net/ethernet/cadence/macb.h      |  1 +
 drivers/net/ethernet/cadence/macb_main.c | 16 ++++++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
index 14dfec4db8f9..989e7c5db9b9 100644
--- a/drivers/net/ethernet/cadence/macb.h
+++ b/drivers/net/ethernet/cadence/macb.h
@@ -1175,6 +1175,7 @@ struct macb_config {
 			    struct clk **hclk, struct clk **tx_clk,
 			    struct clk **rx_clk, struct clk **tsu_clk);
 	int	(*init)(struct platform_device *pdev);
+	unsigned int		max_tx_length;
 	int	jumbo_max_len;
 	const struct macb_usrio_config *usrio;
 };
diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 66e30561569e..1f362bbc360f 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -4095,14 +4095,12 @@ static int macb_init(struct platform_device *pdev)
 
 	/* setup appropriated routines according to adapter type */
 	if (macb_is_gem(bp)) {
-		bp->max_tx_length = GEM_MAX_TX_LEN;
 		bp->macbgem_ops.mog_alloc_rx_buffers = gem_alloc_rx_buffers;
 		bp->macbgem_ops.mog_free_rx_buffers = gem_free_rx_buffers;
 		bp->macbgem_ops.mog_init_rings = gem_init_rings;
 		bp->macbgem_ops.mog_rx = gem_rx;
 		dev->ethtool_ops = &gem_ethtool_ops;
 	} else {
-		bp->max_tx_length = MACB_MAX_TX_LEN;
 		bp->macbgem_ops.mog_alloc_rx_buffers = macb_alloc_rx_buffers;
 		bp->macbgem_ops.mog_free_rx_buffers = macb_free_rx_buffers;
 		bp->macbgem_ops.mog_init_rings = macb_init_rings;
@@ -4839,7 +4837,8 @@ static const struct macb_config mpfs_config = {
 	.clk_init = macb_clk_init,
 	.init = init_reset_optional,
 	.usrio = &macb_default_usrio,
-	.jumbo_max_len = 10240,
+	.max_tx_length = 4040, /* Cadence Erratum 1686 */
+	.jumbo_max_len = 4040,
 };
 
 static const struct macb_config sama7g5_gem_config = {
@@ -4986,8 +4985,17 @@ static int macb_probe(struct platform_device *pdev)
 	bp->tx_clk = tx_clk;
 	bp->rx_clk = rx_clk;
 	bp->tsu_clk = tsu_clk;
-	if (macb_config)
+	if (macb_config) {
+		if (macb_is_gem(bp)) {
+			if (macb_config->max_tx_length)
+				bp->max_tx_length = macb_config->max_tx_length;
+			else
+				bp->max_tx_length = GEM_MAX_TX_LEN;
+		} else {
+			bp->max_tx_length = MACB_MAX_TX_LEN;
+		}
 		bp->jumbo_max_len = macb_config->jumbo_max_len;
+	}
 
 	bp->wol = 0;
 	if (of_property_read_bool(np, "magic-packet"))
-- 
2.25.1