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Subject[PATCH v2 2/2] net: macb: Limit maximum GEM TX length in TSO
GEM_MAX_TX_LEN currently resolves to 0x3FF8 for any IP version supporting
TSO with full 14bits of length field in payload descriptor. But an IP
errata causes false amba_error (bit 6 of ISR) when length in payload
descriptors is specified above 16387. The error occurs because the DMA
falsely concludes that there is not enough space in SRAM for incoming
payload. These errors were observed continuously under stress of large
packets using iperf on a version where SRAM was 16K for each queue. This
errata will be documented shortly and affects all versions since TSO
functionality was added. Hence limit the max length to 0x3FC0 (rounded).

Signed-off-by: Harini Katakam <>
Use 0x3FC0 by default

drivers/net/ethernet/cadence/macb_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 2e418b8..cca321c 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -73,7 +73,7 @@ struct sifive_fu540_macb_mgmt {
/* Max length of transmit frame must be a multiple of 8 bytes */
#define MACB_MAX_TX_LEN ((unsigned int)((1 << MACB_TX_FRMLEN_SIZE) - 1) & ~((unsigned int)(MACB_TX_LEN_ALIGN - 1)))
-#define GEM_MAX_TX_LEN ((unsigned int)((1 << GEM_TX_FRMLEN_SIZE) - 1) & ~((unsigned int)(MACB_TX_LEN_ALIGN - 1)))
+#define GEM_MAX_TX_LEN (unsigned int)(0x3FC0)

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