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@gmail.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);
 	}
 
-- 
2.47.0

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@gmail.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@linux.dev>