linux-kernel - Re: [PATCH net 2/3] broadcom: fix support for PTP_EXTTS

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Message-ID: <fedb5429-2e8d-42df-8080-9a8706407ad2@linux.dev>
Date: Fri, 19 Sep 2025 12:03:33 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jacob Keller <jacob.e.keller@...el.com>,
 Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Andrew Lunn <andrew@...n.ch>,
 Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Kory Maincent <kory.maincent@...tlin.com>
Cc: Richard Cochran <richardcochran@...il.com>,
 Yaroslav Kolomiiets <yrk@...a.com>, James Clark <jjc@...ark.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 2/3] broadcom: fix support for PTP_EXTTS_REQUEST2
 ioctl

On 19/09/2025 01:33, Jacob Keller wrote:
> Commit 7c571ac57d9d ("net: ptp: introduce .supported_extts_flags to
> ptp_clock_info") modified the PTP core kernel logic to validate the
> supported flags for the PTP_EXTTS_REQUEST ioctls, rather than relying on
> each individual driver correctly checking its flags.
> 
> The bcm_ptp_enable() function implements support for PTP_CLK_REQ_EXTTS, but
> does not check the flags, and does not forward the request structure into
> bcm_ptp_extts_locked().
> 
> When originally converting the bcm-phy-ptp.c code, it was unclear what
> edges the hardware actually timestamped. Thus, no flags were initialized in
> the .supported_extts_flags field. This results in the kernel automatically
> rejecting all userspace requests for the PTP_EXTTS_REQUEST2 ioctl.
> 
> This occurs because the PTP_STRICT_FLAGS is always assumed when operating
> under PTP_EXTTS_REQUEST2. This has been the case since the flags
> introduction by commit 6138e687c7b6 ("ptp: Introduce strict checking of
> external time stamp options.").
> 
> The bcm-phy-ptp.c logic never properly supported strict flag validation,
> as it previously ignored all flags including both PTP_STRICT_FLAGS and the
> PTP_FALLING_EDGE and PTP_RISING_EDGE flags.
> 
> Reports from users in the field prove that the hardware timestamps the
> rising edge. Encode this in the .supported_extts_flags field. This
> re-enables support for the PTP_EXTTS_REQUEST2 ioctl.
> 
> Reported-by: James Clark <jjc@...ark.com>
> Fixes: 7c571ac57d9d ("net: ptp: introduce .supported_extts_flags to ptp_clock_info")
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
> ---
>   drivers/net/phy/bcm-phy-ptp.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/phy/bcm-phy-ptp.c b/drivers/net/phy/bcm-phy-ptp.c
> index 1cf695ac73cc..d3501f8487d9 100644
> --- a/drivers/net/phy/bcm-phy-ptp.c
> +++ b/drivers/net/phy/bcm-phy-ptp.c
> @@ -738,6 +738,7 @@ static const struct ptp_clock_info bcm_ptp_clock_info = {
>   	.n_per_out	= 1,
>   	.n_ext_ts	= 1,
>   	.supported_perout_flags = PTP_PEROUT_DUTY_CYCLE,
> +	.supported_extts_flags = PTP_STRICT_FLAGS | PTP_RISING_EDGE,
>   };
>   
>   static void bcm_ptp_txtstamp(struct mii_timestamper *mii_ts,
> 

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>