linux-kernel - Re: [PATCH v5 net-next 05/15] ptp: netc: add PTP_CLK_REQ

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Message-ID: <aKx8rPX0uvRaP0KB@lizhi-Precision-Tower-5810>
Date: Mon, 25 Aug 2025 11:09:32 -0400
From: Frank Li <Frank.li@....com>
To: Wei Fang <wei.fang@....com>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	richardcochran@...il.com, claudiu.manoil@....com,
	vladimir.oltean@....com, xiaoning.wang@....com,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, vadim.fedorenko@...ux.dev,
	shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com,
	fushi.peng@....com, devicetree@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	imx@...ts.linux.dev, kernel@...gutronix.de
Subject: Re: [PATCH v5 net-next 05/15] ptp: netc: add PTP_CLK_REQ_PPS support

On Mon, Aug 25, 2025 at 12:15:22PM +0800, Wei Fang wrote:
> The NETC Timer is capable of generating a PPS interrupt to the host. To
> support this feature, a 64-bit alarm time (which is a integral second
> of PHC in the future) is set to TMR_ALARM, and the period is set to
> TMR_FIPER. The alarm time is compared to the current time on each update,
> then the alarm trigger is used as an indication to the TMR_FIPER starts
> down counting. After the period has passed, the PPS event is generated.
>
> According to the NETC block guide, the Timer has three FIPERs, any of
> which can be used to generate the PPS events, but in the current
> implementation, we only need one of them to implement the PPS feature,
> so FIPER 0 is used as the default PPS generator. Also, the Timer has
> 2 ALARMs, currently, ALARM 0 is used as the default time comparator.
>
> However, if the time is adjusted or the integer of period is changed when
> PPS is enabled, the PPS event will not be generated at an integral second
> of PHC. The suggested steps from IP team if time drift happens:
>
> 1. Disable FIPER before adjusting the hardware time
> 2. Rearm ALARM after the time adjustment to make the next PPS event be
> generated at an integral second of PHC.
> 3. Re-enable FIPER.
>
> Signed-off-by: Wei Fang <wei.fang@....com>

Reviewed-by: Frank Li <Frank.Li@....com>

>
> ---
> v5 changes:
> 1. Fix irq name issue, since request_irq() does not copy the name from
>    irq_name.
> v4 changes:
> 1. Improve the commit message, the PPS generation time will be inaccurate
>    if the time is adjusted or the integer of period is changed.
> v3 changes:
> 1. Use "2 * NSEC_PER_SEC" to instead of "2000000000U"
> 2. Improve the commit message
> 3. Add alarm related logic and the irq handler
> 4. Add tmr_emask to struct netc_timer to save the irq masks instead of
>    reading TMR_EMASK register
> 5. Remove pps_channel from struct netc_timer and remove
>    NETC_TMR_DEFAULT_PPS_CHANNEL
> v2 changes:
> 1. Refine the subject and the commit message
> 2. Add a comment to netc_timer_enable_pps()
> 3. Remove the "nxp,pps-channel" logic from the driver
> ---
>  drivers/ptp/ptp_netc.c | 262 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 259 insertions(+), 3 deletions(-)
>
...
>
> --
> 2.34.1
>