The MMCSR register contains 2 fields with overlapping meaning: - LPA (Local preemption active): This read-only status bit indicates whether preemption is active for this port. This bit will be set if preemption is both enabled and has completed the verification process. - TXSTS (Merge status): This read-only status field provides the state of the MAC Merge sublayer transmit status as defined in IEEE Std 802.3-2018 Clause 99. 00 Transmit preemption is inactive 01 Transmit preemption is active 10 Reserved 11 Reserved However none of these 2 fields offer reliable reporting to software. When connecting ENETC to a link partner which is not capable of Frame Preemption, the expectation is that ENETC's verification should fail (VSTS=4) and its MM TX direction should be inactive (LPA=0, TXSTS=00) even though the MM TX is enabled (ME=1). But surprise, the LPA bit of MMCSR stays set even if VSTS=4 and ME=1. OTOH, the TXSTS field has the opposite problem. I cannot get its value to change from 0, even when connecting to a link partner capable of frame preemption, which does respond to its verification frames (ME=1 and VSTS=3, "SUCCEEDED"). The only option with such buggy hardware seems to be to reimplement the formula for calculating tx-active in software, which is for tx-enabled to be true, and for the verify-status to be either SUCCEEDED, or DISABLED. Without reliable tx-active reporting, we have no good indication when to commit the preemptible traffic classes to hardware, which makes it possible (but not desirable) to send preemptible traffic to a link partner incapable of receiving it. However, currently we do not have the logic to wait for TX to be active yet, so the impact is limited. Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx> --- v1->v2: patch is new drivers/net/ethernet/freescale/enetc/enetc_ethtool.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c index ee1ea71fe79e..deb674752851 100644 --- a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c +++ b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c @@ -976,7 +976,9 @@ static int enetc_get_mm(struct net_device *ndev, struct ethtool_mm_state *state) lafs = ENETC_MMCSR_GET_LAFS(val); state->rx_min_frag_size = ethtool_mm_frag_size_add_to_min(lafs); state->tx_enabled = !!(val & ENETC_MMCSR_LPE); /* mirror of MMCSR_ME */ - state->tx_active = !!(val & ENETC_MMCSR_LPA); + state->tx_active = state->tx_enabled && + (state->verify_status == ETHTOOL_MM_VERIFY_STATUS_SUCCEEDED || + state->verify_status == ETHTOOL_MM_VERIFY_STATUS_DISABLED); state->verify_enabled = !(val & ENETC_MMCSR_VDIS); state->verify_time = ENETC_MMCSR_GET_VT(val); /* A verifyTime of 128 ms would exceed the 7 bit width -- 2.34.1
