Re: [PATCH net RESEND 2/2] net: macb: Use all-frame timestamping for PTPv1 RX filters

[Paolo Abeni <pabeni@redhat.com>]

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---
net: macb: Use all-frame timestamping for PTPv1 RX filters

The two PTPv1 L4 filters used to be accepted by gem_set_hwtst() while
leaving rx_bd_control at TSTAMP_DISABLED, so receive timestamping ended up
off even though a nonempty filter was reported back. They are now folded
into the existing all-frame arm alongside HWTSTAMP_FILTER_PTP_V1_L4_EVENT,
which reports HWTSTAMP_FILTER_ALL.

No Link: tags in the commit header.

A few observations on the surrounding code in gem_set_hwtst(), all of them
about behaviour that predates this change.

> diff --git a/drivers/net/ethernet/cadence/macb_ptp.c b/drivers/net/ethernet/cadence/macb_ptp.c
> index 51659bbdfac9a..2ffc46b81264e 100644
> --- a/drivers/net/ethernet/cadence/macb_ptp.c
> +++ b/drivers/net/ethernet/cadence/macb_ptp.c
> @@ -430,10 +430,6 @@ int gem_set_hwtst(struct net_device *netdev,
>  	switch (tstamp_config->rx_filter) {
>  	case HWTSTAMP_FILTER_NONE:
>  		break;
> -	case HWTSTAMP_FILTER_PTP_V1_L4_SYNC:
> -		break;
> -	case HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ:
> -		break;
>  	case HWTSTAMP_FILTER_PTP_V2_EVENT:
>  	case HWTSTAMP_FILTER_PTP_V2_L2_EVENT:
>  	case HWTSTAMP_FILTER_PTP_V2_L4_EVENT:

[Severity: Medium]
This isn't a bug introduced by this patch, but while the new arm reports
HWTSTAMP_FILTER_ALL (which is advertised), the sibling PTPv2 arm right below
reports a filter value the driver never advertises:

drivers/net/ethernet/cadence/macb_main.c:gem_get_ts_info() {
	info->rx_filters =
		(1 << HWTSTAMP_FILTER_NONE) |
		(1 << HWTSTAMP_FILTER_ALL);
}

drivers/net/ethernet/cadence/macb_ptp.c:gem_set_hwtst() {
		rx_bd_control =  TSTAMP_ALL_PTP_FRAMES;
		tstamp_config->rx_filter = HWTSTAMP_FILTER_PTP_V2_EVENT;
}

That value is then stored in bp->tstamp_config and handed back by
gem_get_hwtst() on every later SIOCGHWTSTAMP, so ethtool -T and
SIOCGHWTSTAMP describe different capability sets. Should the PTPv2 arm
either report HWTSTAMP_FILTER_ALL too, or should gem_get_ts_info() advertise
HWTSTAMP_FILTER_PTP_V2_EVENT?

> @@ -448,6 +444,8 @@ int gem_set_hwtst(struct net_device *netdev,
>  		regval = macb_readl(bp, NCR);
>  		macb_writel(bp, NCR, (regval | MACB_BIT(SRTSM)));

[Severity: High]
This is a pre-existing issue and not something this patch introduces, but is
this read-modify-write of NCR safe without bp->lock? Every other NCR
read-modify-write in the driver is serialized, and macb_tx_lpi_set() even
states the rule:

drivers/net/ethernet/cadence/macb_main.c:macb_tx_lpi_set() {
	lockdep_assert_held(&bp->lock);

	ncr = macb_readl(bp, NCR);
	old = ncr;
	...
}

drivers/net/ethernet/cadence/macb_main.c:macb_start_xmit() {
	spin_lock(&bp->lock);
	macb_tx_lpi_wake(bp);
	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
	spin_unlock(&bp->lock);
}

gem_set_hwtst() runs under rtnl from ndo_hwtstamp_set, which does not
exclude the xmit path, the EEE LPI work, macb_mac_link_up(), or the hardirq
RXUBR workaround. Can the unlocked write back lose a bit another context
just set? For example the RXUBR errata path in macb_interrupt() toggles RE:

drivers/net/ethernet/cadence/macb_main.c:macb_interrupt() {
		ctrl = macb_readl(bp, NCR);
		macb_writel(bp, NCR, ctrl & ~MACB_BIT(RE));
		wmb();
		macb_writel(bp, NCR, ctrl | MACB_BIT(RE));
}

If gem_set_hwtst() samples NCR inside that window and then writes back with
RE cleared, does receive stay off until the next reconfiguration? The same
question applies to gem_ptp_set_one_step_sync(), which this function calls
for TX_ON and ONESTEP_SYNC, including for the two filters added here:

drivers/net/ethernet/cadence/macb_ptp.c:gem_ptp_set_one_step_sync() {
	reg_val = macb_readl(bp, NCR);

	if (enable)
		macb_writel(bp, NCR, reg_val | MACB_BIT(OSSMODE));
	else
		macb_writel(bp, NCR, reg_val & ~MACB_BIT(OSSMODE));
}

Since the RXUBR handler runs in hardirq context, would the irqsave variant
of the lock be needed on the configuration side?

>  		break;
> +	case HWTSTAMP_FILTER_PTP_V1_L4_SYNC:
> +	case HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ:
>  	case HWTSTAMP_FILTER_PTP_V1_L4_EVENT:
>  	case HWTSTAMP_FILTER_ALL:
>  		rx_bd_control = TSTAMP_ALL_FRAMES;

Two more items in the same function and driver, outside the hunks:

[Severity: Medium]
This is a pre-existing issue that this patch does not touch, but in
gem_set_hwtst() the HWTSTAMP_TX_OFF arm is a bare break:

	switch (tstamp_config->tx_type) {
	case HWTSTAMP_TX_OFF:
		break;
	case HWTSTAMP_TX_ONESTEP_SYNC:
		tx_bd_control = TSTAMP_ALL_FRAMES;
		break;

and OSSMODE is only touched for the other two values:

	if (tstamp_config->tx_type == HWTSTAMP_TX_ONESTEP_SYNC)
		gem_ptp_set_one_step_sync(bp, 1);
	else if (tstamp_config->tx_type == HWTSTAMP_TX_ON)
		gem_ptp_set_one_step_sync(bp, 0);

After HWTSTAMP_TX_ONESTEP_SYNC followed by HWTSTAMP_TX_OFF, does NCR.OSSMODE
stay set so the MAC keeps rewriting originTimestamp in transmitted Sync
frames while SIOCGHWTSTAMP reports transmit timestamping as off? Should the
TX_OFF case call gem_ptp_set_one_step_sync(bp, 0) as well? The symmetric
case, NCR.SRTSM never being cleared when moving away from the PTPv2 arm,
looks like the same shape of problem.

[Severity: Medium]
Also pre-existing rather than something this patch changes: is the
timestamping configuration lost across suspend/resume? macb_resume()
rewrites NCR from scratch:

drivers/net/ethernet/cadence/macb_main.c:macb_resume() {
	macb_writel(bp, NCR, MACB_BIT(MPE));
	macb_init_hw(bp);
	macb_set_rx_mode(netdev);
	macb_restore_features(bp);
	...
}

which clears SRTSM and OSSMODE, and none of the callees reprogram the
descriptor capture registers. gem_ptp_set_ts_mode() is the only writer of
GEM_TXBDCTRL and GEM_RXBDCTRL:

drivers/net/ethernet/cadence/macb_ptp.c:gem_ptp_set_ts_mode() {
	gem_writel(bp, TXBDCTRL, GEM_BF(TXTSMODE, tx_bd_control));
	gem_writel(bp, RXBDCTRL, GEM_BF(RXTSMODE, rx_bd_control));
}

and it is reachable only from gem_set_hwtst(). Does that leave the hardware
at its reset default after resume while gem_get_hwtst() still reports the
pre-suspend filter, now including HWTSTAMP_FILTER_ALL for the two PTPv1
filters remapped here? Should the resume path replay bp->tstamp_config
through gem_ptp_set_ts_mode()?
-- 
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