git: f09f2763b67f - stable/13 - igc: sync srrctl buffer sizing with e1000

The branch stable/13 has been updated by kbowling:

URL: https://cgit.FreeBSD.org/src/commit/?id=f09f2763b67fcbf65d7cac5b114eab72308cde60

commit f09f2763b67fcbf65d7cac5b114eab72308cde60
Author:     Kevin Bowling <kbowling@FreeBSD.org>
AuthorDate: 2023-08-10 14:41:21 +0000
Commit:     Kevin Bowling <kbowling@FreeBSD.org>
CommitDate: 2023-08-17 00:30:32 +0000

    igc: sync srrctl buffer sizing with e1000
    
    Approved by:    grehan
    Differential Revision:  https://reviews.freebsd.org/D31493
    
    (cherry picked from commit 0eb8cd1de26849cbaefaf3bc59aa9612fa0dfa52)
---
 sys/dev/igc/if_igc.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/sys/dev/igc/if_igc.c b/sys/dev/igc/if_igc.c
index 826a35e7e15e..49d4755d057c 100644
--- a/sys/dev/igc/if_igc.c
+++ b/sys/dev/igc/if_igc.c
@@ -1986,6 +1986,7 @@ igc_initialize_transmit_unit(if_ctx_t ctx)
  *  Enable receive unit.
  *
  **********************************************************************/
+#define BSIZEPKT_ROUNDUP	((1<<IGC_SRRCTL_BSIZEPKT_SHIFT)-1)
 
 static void
 igc_initialize_receive_unit(if_ctx_t ctx)
@@ -2051,24 +2052,19 @@ igc_initialize_receive_unit(if_ctx_t ctx)
 		igc_initialize_rss_mapping(adapter);
 
 	if (if_getmtu(ifp) > ETHERMTU) {
-		/* Set maximum packet len */
-		if (adapter->rx_mbuf_sz <= 4096) {
-			srrctl |= 4096 >> IGC_SRRCTL_BSIZEPKT_SHIFT;
-			rctl |= IGC_RCTL_SZ_4096 | IGC_RCTL_BSEX;
-		} else if (adapter->rx_mbuf_sz > 4096) {
-			srrctl |= 8192 >> IGC_SRRCTL_BSIZEPKT_SHIFT;
-			rctl |= IGC_RCTL_SZ_8192 | IGC_RCTL_BSEX;
-		}
 		psize = scctx->isc_max_frame_size;
 		/* are we on a vlan? */
 		if (ifp->if_vlantrunk != NULL)
 			psize += VLAN_TAG_SIZE;
 		IGC_WRITE_REG(&adapter->hw, IGC_RLPML, psize);
-	} else {
-		srrctl |= 2048 >> IGC_SRRCTL_BSIZEPKT_SHIFT;
-		rctl |= IGC_RCTL_SZ_2048;
 	}
 
+	/* Set maximum packet buffer len */
+	srrctl |= (adapter->rx_mbuf_sz + BSIZEPKT_ROUNDUP) >>
+	    IGC_SRRCTL_BSIZEPKT_SHIFT;
+	/* srrctl above overrides this but set the register to a sane value */
+	rctl |= IGC_RCTL_SZ_2048;
+
 	/*
 	 * If TX flow control is disabled and there's >1 queue defined,
 	 * enable DROP.