[PATCH 6.18 026/227] igc: Reduce TSN TX packet buffer from 7KB to 5KB per queue

Greg Kroah-Hartman
2026-01-28T15:51:36Z

From: Chwee-Lin Choong <chwee.lin.choong@intel.com>

[ Upstream commit 8ad1b6c1e63d25f5465b7a8aa403bdcee84b86f9 ]

The previous 7 KB per queue caused TX unit hangs under heavy
timestamping load. Reducing to 5 KB avoids these hangs and matches
the TSN recommendation in I225/I226 SW User Manual Section 7.5.4.

The 8 KB "freed" by this change is currently unused. This reduction
is not expected to impact throughput, as the i226 is PCIe-limited
for small TSN packets rather than TX-buffer-limited.

Fixes: 0d58cdc902da ("igc: optimize TX packet buffer utilization for TSN mode")
Reported-by: Zdenek Bouska <zdenek.bouska@siemens.com>
Closes: https://lore.kernel.org/netdev/AS1PR10MB5675DBFE7CE5F2A9336ABFA4EBEAA@AS1PR10MB5675.EURPRD10.PROD.OUTLOOK.COM/
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/intel/igc/igc_defines.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_defines.h b/drivers/net/ethernet/intel/igc/igc_defines.h
index 498ba1522ca4d..9482ab11f050f 100644
--- a/drivers/net/ethernet/intel/igc/igc_defines.h
+++ b/drivers/net/ethernet/intel/igc/igc_defines.h
@@ -443,9 +443,10 @@
#define IGC_TXPBSIZE_DEFAULT ( \
IGC_TXPB0SIZE(20) | IGC_TXPB1SIZE(0) | IGC_TXPB2SIZE(0) | \
IGC_TXPB3SIZE(0) | IGC_OS2BMCPBSIZE(4))
+/* TSN value following I225/I226 SW User Manual Section 7.5.4 */
#define IGC_TXPBSIZE_TSN ( \
- IGC_TXPB0SIZE(7) | IGC_TXPB1SIZE(7) | IGC_TXPB2SIZE(7) | \
- IGC_TXPB3SIZE(7) | IGC_OS2BMCPBSIZE(4))
+ IGC_TXPB0SIZE(5) | IGC_TXPB1SIZE(5) | IGC_TXPB2SIZE(5) | \
+ IGC_TXPB3SIZE(5) | IGC_OS2BMCPBSIZE(4))

#define IGC_DTXMXPKTSZ_TSN 0x19 /* 1600 bytes of max TX DMA packet size */
#define IGC_DTXMXPKTSZ_DEFAULT 0x98 /* 9728-byte Jumbo frames */
--
2.51.0