bnxt_en: Report the ethtool coredump length after copying the coredump

JIRA: https://issues.redhat.com/browse/RHEL-76565

commit c21c8e1
Author: Shruti Parab <shruti.parab@broadcom.com>
Date:   Thu Apr 17 10:24:46 2025 -0700

    bnxt_en: Report the ethtool coredump length after copying the coredump

    ethtool first calls .get_dump_flags() to get the dump length.  For
    coredump, the driver calls the FW to get the coredump length (L1).  The
    min. of L1 and the user specified length is then passed to
    .get_dump_data() (L2) to get the coredump.  The actual coredump length
    retrieved by the FW (L3) during .get_dump_data() may be smaller than L1.
    This length discrepancy will trigger a WARN_ON() in
    ethtool_get_dump_data().

    ethtool has already vzalloc'ed a buffer with size L1.  Just report
    the coredump length as L2 even though the actual coredump length L3
    may be smaller.  The extra zero padding does not matter.  This will
    prevent the warning that may alarm the user.

    For correctness, only do the final length update if there is no error.

    Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
    Reviewed-by: Damodharam Ammepalli <damodharam.ammepalli@broadcom.com>
    Signed-off-by: Shruti Parab <shruti.parab@broadcom.com>
    Signed-off-by: Michael Chan <michael.chan@broadcom.com>
    Link: https://patch.msgid.link/20250417172448.1206107-3-michael.chan@broadcom.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Shruti Parab <shruti.parab@broadcom.com>

Author: Shruti Parab

drivers/net/ethernet/broadcom/bnxt/bnxt_coredump.c

@@ -496,9 +496,16 @@ static int __bnxt_get_coredump(struct bnxt *bp, u16 dump_type, void *buf,
 					  start_utc, coredump.total_segs + 1,
 					  rc);
 	kfree(coredump.data);
-	*dump_len += sizeof(struct bnxt_coredump_record);
-	if (rc == -ENOBUFS)
+	if (!rc) {
+		*dump_len += sizeof(struct bnxt_coredump_record);
+		/* The actual coredump length can be smaller than the FW
+		 * reported length earlier.  Use the ethtool provided length.
+		 */
+		if (buf_len)
+			*dump_len = buf_len;
+	} else if (rc == -ENOBUFS) {
 		netdev_err(bp->dev, "Firmware returned large coredump buffer\n");
+	}
 	return rc;
 }