[PATCH v2] net: ti: icssg-prueth: Fix tx_total_bytes count

[MD Danish Anwar <danishanwar@ti.com>]

ICSSG HW stats on TX side considers 8 preamble bytes as data bytes. Due
to this the tx_bytes of ICSSG interface doesn't match the rx_bytes of the
link partner. There is no public errata available yet.

As a workaround to fix this, decrease tx_bytes by 8 bytes for every tx
frame.

Fixes: c1e10d5dc7a1 ("net: ti: icssg-prueth: Add ICSSG Stats")
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
---
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Ravi Gunasekaran <r-gunasekaran@ti.com>

Changes from v1 to v2:
*) Rebased on the latest net/main.
*) Changed stats name comparison to stats offset comparison as asked by
   Andrew.
*) Modified commit message as asked by Ravi.

v1: https://lore.kernel.org/all/20231011063700.1824093-1-danishanwar@ti.com/

 drivers/net/ethernet/ti/icssg/icssg_stats.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/ti/icssg/icssg_stats.c b/drivers/net/ethernet/ti/icssg/icssg_stats.c
index bb0b33927e3b..3dbadddd7e35 100644
--- a/drivers/net/ethernet/ti/icssg/icssg_stats.c
+++ b/drivers/net/ethernet/ti/icssg/icssg_stats.c
@@ -9,6 +9,9 @@
 #include "icssg_stats.h"
 #include <linux/regmap.h>
 
+#define ICSSG_TX_PACKET_OFFSET	0xA0
+#define ICSSG_TX_BYTE_OFFSET	0xEC
+
 static u32 stats_base[] = {	0x54c,	/* Slice 0 stats start */
 				0xb18,	/* Slice 1 stats start */
 };
@@ -18,6 +21,7 @@ void emac_update_hardware_stats(struct prueth_emac *emac)
 	struct prueth *prueth = emac->prueth;
 	int slice = prueth_emac_slice(emac);
 	u32 base = stats_base[slice];
+	u32 tx_pkt_cnt = 0;
 	u32 val;
 	int i;
 
@@ -29,7 +33,12 @@ void emac_update_hardware_stats(struct prueth_emac *emac)
 			     base + icssg_all_stats[i].offset,
 			     val);
 
+		if (icssg_all_stats[i].offset == ICSSG_TX_PACKET_OFFSET)
+			tx_pkt_cnt = val;
+
 		emac->stats[i] += val;
+		if (icssg_all_stats[i].offset == ICSSG_TX_BYTE_OFFSET)
+			emac->stats[i] -= tx_pkt_cnt * 8;
 	}
 }

base-commit: 71c299c711d1f44f0bf04f1fea66baad565240f1 
-- 
2.34.1