linux-kernel - Re: [PATCH v2] ptp: ocp: fix start time alignment in ptp_ocp_signal

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Message-ID: <68769daa-fbd5-4dbd-87a6-5b74bdc20094@linux.dev>
Date: Tue, 15 Apr 2025 08:51:13 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Sagi Maimon <maimon.sagi@...il.com>, jonathan.lemon@...il.com,
 richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] ptp: ocp: fix start time alignment in
 ptp_ocp_signal_set

On 15/04/2025 06:31, Sagi Maimon wrote:
> In ptp_ocp_signal_set, the start time for periodic signals is not
> aligned to the next period boundary. The current code rounds up the
> start time and divides by the period but fails to multiply back by
> the period, causing misaligned signal starts. Fix this by multiplying
> the rounded-up value by the period to ensure the start time is the
> closest next period.
> 
> Fixes: 4bd46bb037f8e ("ptp: ocp: Use DIV64_U64_ROUND_UP for rounding.")
> Signed-off-by: Sagi Maimon <maimon.sagi@...il.com>
> ---
>   Addressed comments from Vadim Fedorenko:
>   - https://www.spinics.net/lists/netdev/msg1083572.html
>   Changes since version 1:
>   - Simplified multiplication in expression by removing unnecessary parentheses
>     and using compound assignment operator, as suggested by the maintainer.
> ---
>   drivers/ptp/ptp_ocp.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> index 7945c6be1f7c..faf6e027f89a 100644
> --- a/drivers/ptp/ptp_ocp.c
> +++ b/drivers/ptp/ptp_ocp.c
> @@ -2067,6 +2067,7 @@ ptp_ocp_signal_set(struct ptp_ocp *bp, int gen, struct ptp_ocp_signal *s)
>   	if (!s->start) {
>   		/* roundup() does not work on 32-bit systems */
>   		s->start = DIV64_U64_ROUND_UP(start_ns, s->period);
> +		s->start *= s->period;
>   		s->start = ktime_add(s->start, s->phase);
>   	}
>   
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>