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Subject[PATCH net-next v1 1/1] net: macb: fix negative max_mtu size for sama5d3
Date
On Microchip SAMA5D3 the JML will return null. So, after header and FCS length
subtraction we will get negative max_mtu size. This issue was directly
affecting DSA drivers with MTU support (for example KSZ9477).

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
drivers/net/ethernet/cadence/macb_main.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index d89098f4ede8..c7e1c9ac9809 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -4913,10 +4913,24 @@ static int macb_probe(struct platform_device *pdev)

/* MTU range: 68 - 1500 or 10240 */
dev->min_mtu = GEM_MTU_MIN_SIZE;
- if (bp->caps & MACB_CAPS_JUMBO)
- dev->max_mtu = gem_readl(bp, JML) - ETH_HLEN - ETH_FCS_LEN;
- else
+ if (bp->caps & MACB_CAPS_JUMBO) {
+ u32 val;
+
+ if (bp->jumbo_max_len)
+ val = bp->jumbo_max_len;
+ else
+ val = gem_readl(bp, JML);
+
+ if (val < ETH_DATA_LEN) {
+ dev_warn(&pdev->dev, "Suspicious max MTU size (%u), overwriting to %u\n",
+ val, ETH_DATA_LEN);
+ dev->max_mtu = ETH_DATA_LEN;
+ } else {
+ dev->max_mtu = val - ETH_HLEN - ETH_FCS_LEN;
+ }
+ } else {
dev->max_mtu = ETH_DATA_LEN;
+ }

if (bp->caps & MACB_CAPS_BD_RD_PREFETCH) {
val = GEM_BFEXT(RXBD_RDBUFF, gem_readl(bp, DCFG10));
--
2.30.2
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