Re: [PATCH net v2 2/3] net: txgbe: keep MAC enabled for SP devices that support NCSI

[netdev-bot+sashiko@kernel.org]

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- [Medium] The fix covers only one of the phylink callbacks that turn off
  the MAC transmitter.

Pre-existing issues:
- [Low] At this patch, txgbe_mac_link_down_aml() in
  drivers/net/ethernet/wangxun/txgbe/txgbe_aml.c (lines 455-468) still…
- [Low] The new condition in txgbe_mac_link_down() (txgbe_phy.c:185)
  exempts only NCSI devices.

--

net: txgbe: keep MAC enabled for SP devices that support NCSI

This patch makes txgbe_mac_link_down() stop clearing WX_MAC_TX_CFG_TE when
the subsystem device ID shows NCSI support. The aim is to keep the MAC
transmitter on after link-down on SP devices, so NCSI keeps working.
Other devices keep the existing link-down handling.

> diff --git a/drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c b/drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c
> index dc9f243146580..d11f26dc13e92 100644
> --- a/drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c
> +++ b/drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c
> @@ -182,7 +182,8 @@ static void txgbe_mac_link_down(struct phylink_config *config,
>  {
>  	struct wx *wx = phylink_to_wx(config);
>  
> -	wr32m(wx, WX_MAC_TX_CFG, WX_MAC_TX_CFG_TE, 0);
> +	if (!((wx->subsystem_device_id & WX_NCSI_MASK) == WX_NCSI_SUP))
> +		wr32m(wx, WX_MAC_TX_CFG, WX_MAC_TX_CFG_TE, 0);

[Severity: Medium]
Does this keep the transmitter on for NCSI boards in all cases? Another
callback in the same txgbe_mac_ops still clears TE with no NCSI check:

drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c:txgbe_mac_prepare() {
    ...
	wr32m(wx, WX_MAC_TX_CFG, WX_MAC_TX_CFG_TE, 0);
	wr32m(wx, WX_MAC_RX_CFG, WX_MAC_RX_CFG_RE, 0);
    ...
}

txgbe_mac_finish() turns the SEC TX path and MAC RX back on, but not TE:

drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c:txgbe_mac_finish() {
    ...
	txgbe_enable_sec_tx_path(wx);
	wr32m(wx, WX_MAC_RX_CFG, WX_MAC_RX_CFG_RE, WX_MAC_RX_CFG_RE);
    ...
}

So TE is only set again in txgbe_mac_link_up().

mac_prepare runs on every major config, before any link is resolved:

phylink_start()
  phylink_mac_initial_config()
    phylink_major_config()
      txgbe_mac_prepare()

Resume and SFP interface changes also reach this path.

Here is a sequence on an NCSI SP board:

1. ifup with no cable. txgbe_mac_prepare() clears TE. The link never
   comes up, so txgbe_mac_link_up() never runs.

2. ifdown. phylink_stop() only calls mac_link_down if the link was up,
   so it isn't called. txgbe_disable_device() skips clearing TE for NCSI,
   but it doesn't set TE either:

	if (!(((wx->subsystem_device_id & WX_NCSI_MASK) == WX_NCSI_SUP) ||
	      ((wx->subsystem_device_id & WX_WOL_MASK) == WX_WOL_SUP))) {
		/* disable mac transmiter */
		wr32m(wx, WX_MAC_TX_CFG, WX_MAC_TX_CFG_TE, 0);
	}

3. The host interface stays down with TE=0. If a cable is plugged in
   later, BMC pass-through transmit would still be blocked.

Even on a normal ifup, BMC transmit appears to be blocked from
mac_prepare until link-up.

I couldn't tell from the code whether firmware or a hardware reset turns
TE back on in this state. On copper, txgbe_reset_hw() doesn't issue a
LAN reset.

The follow-up patch "net: txgbe: keep MAC enabled for AML devices that
support NCSI" only touches txgbe_aml.c. That means txgbe_mac_prepare()
and txgbe_mac_finish() are still unchanged at the end of the series.

When (subsystem_device_id & WX_NCSI_MASK) == WX_NCSI_SUP, should
txgbe_mac_prepare() leave TE set, or should txgbe_mac_finish() set it
again?

[Severity: Low]
This isn't a bug introduced by this patch. At this point in the series,
the AML link-down callback still clears both TX and RX on NCSI devices:

drivers/net/ethernet/wangxun/txgbe/txgbe_aml.c:txgbe_mac_link_down_aml() {
    ...
	wr32m(wx, TXGBE_AML_MAC_TX_CFG, TXGBE_AML_MAC_TX_CFG_TE, 0);
	wr32m(wx, WX_MAC_RX_CFG, WX_MAC_RX_CFG_RE, 0);
    ...
}

The next patch in the series, "net: txgbe: keep MAC enabled for AML
devices that support NCSI", wraps both writes in the same NCSI check.
This looks resolved once the whole series is applied.

[Severity: Low]
This is a pre-existing inconsistency, not something this patch
introduced. The new check only tests WX_NCSI_SUP. txgbe_disable_device()
exempts both NCSI and WOL boards from clearing the same TE bit (see the
snippet above).

This patch doesn't change anything for WOL-only boards. WOL relies on
MAC RX, which wx_disable_rx() keeps on, and txgbe doesn't implement WOL.
So I don't see a functional effect.

Is the difference between the two conditions intentional?

[ ... ]

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