| Message ID | 20230418111459.811553-3-vladimir.oltean@nxp.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 153b5b1d030de3f94ecac4eec73854e4710ca6ba |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | ethtool mm API consolidation | expand |
On Tue, Apr 18, 2023 at 02:14:52PM +0300, Vladimir Oltean wrote: > 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@nxp.com> Reviewed-by: Simon Horman <simon.horman@corigine.com>
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
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@nxp.com> --- v1->v2: patch is new drivers/net/ethernet/freescale/enetc/enetc_ethtool.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)