linux-kernel - Re: [PATCH net-next 2/3] ptp: netc: add the periodic output signal loopback support

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Message-ID: <20250904133150.shxehnjfz2qpl2dk@skbuf>
Date: Thu, 4 Sep 2025 16:31:50 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: Wei Fang <wei.fang@....com>
Cc: richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	xiaoning.wang@....com, Frank.Li@....com, yangbo.lu@....com,
	christophe.leroy@...roup.eu, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev
Subject: Re: [PATCH net-next 2/3] ptp: netc: add the periodic output signal
 loopback support

On Wed, Sep 03, 2025 at 04:37:48PM +0800, Wei Fang wrote:
> The NETC Timer supports looping back the output pulse signal of Fiper-n
> into Trigger-n input, so that users can leverage this feature to validate
> some other features without external hardware support. For example, users
> can use it to test external trigger stamp (EXTTS). And users can combine
> EXTTS with loopback mode to check whether the generation time of PPS is
> aligned with an integral second of PHC, or the periodic output signal
> (PTP_CLK_REQ_PEROUT) whether is generated at the specified time.
> 
> Since ptp_clock_info::perout_loopback() has been added to the ptp_clock
> driver as a generic interface to enable or disable the periodic output
> signal loopback, therefore, netc_timer_perout_loopback() is added as a
> callback of ptp_clock_info::perout_loopback().
> 
> Test the generation time of PPS event:
> 
> $ echo 0 1 > /sys/kernel/debug/ptp0/perout_loopback
> $ echo 1 > /sys/class/ptp/ptp0/pps_enable
> $ testptp -d /dev/ptp0 -e 3
> external time stamp request okay
> event index 0 at 63.000000017
> event index 0 at 64.000000017
> event index 0 at 65.000000017
> 
> Test the generation time of the periodic output signal:
> 
> $ echo 0 1 > /sys/kernel/debug/ptp0/perout_loopback
> $ echo 0 150 0 1 500000000 > /sys/class/ptp/ptp0/period
> $ testptp -d /dev/ptp0 -e 3
> external time stamp request okay
> event index 0 at 150.000000014
> event index 0 at 151.500000015
> event index 0 at 153.000000014
> 
> Signed-off-by: Wei Fang <wei.fang@....com>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@....com>