netdev - Re: [PATCH net] ptp: ocp: have adjtime handle negative delta

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Message-ID: <a07b0326-19c7-5756-106c-28b52975871d@novek.ru>
Date:   Sat, 7 May 2022 01:19:54 +0100
From:   Vadim Fedorenko <vfedorenko@...ek.ru>
To:     Jonathan Lemon <jonathan.lemon@...il.com>, netdev@...r.kernel.org
Cc:     richardcochran@...il.com, kernel-team@...com, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com
Subject: Re: [PATCH net] ptp: ocp: have adjtime handle negative delta_ns
 correctly

On 06.05.2022 00:40, Jonathan Lemon wrote:
> delta_ns is a s64, but it was being passed ptp_ocp_adjtime_coarse
> as an u64.  Also, it turns out that timespec64_add_ns() only handles
> positive values, so the math needs to be updated.
> 
> Fix by passing in the correct signed value, then adding to a
> nanosecond version of the timespec.
> 
> Fixes: '90f8f4c0e3ce ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")'
> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> ---
>   drivers/ptp/ptp_ocp.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> index dd45471f6780..65e592ec272e 100644
> --- a/drivers/ptp/ptp_ocp.c
> +++ b/drivers/ptp/ptp_ocp.c
> @@ -841,16 +841,18 @@ __ptp_ocp_adjtime_locked(struct ptp_ocp *bp, u32 adj_val)
>   }
>   
>   static void
> -ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, u64 delta_ns)
> +ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, s64 delta_ns)
>   {
>   	struct timespec64 ts;
>   	unsigned long flags;
>   	int err;
> +	s64 ns;
>   
>   	spin_lock_irqsave(&bp->lock, flags);
>   	err = __ptp_ocp_gettime_locked(bp, &ts, NULL);
>   	if (likely(!err)) {
> -		timespec64_add_ns(&ts, delta_ns);
> +		ns = timespec64_to_ns(&ts) + delta_ns;
> +		ts = ns_to_timespec64(ns);

Maybe use set_normalized_timespec64 instead of this ugly transformations and 
additional variable?

>   		__ptp_ocp_settime_locked(bp, &ts);
>   	}
>   	spin_unlock_irqrestore(&bp->lock, flags);