linux-kernel - Re: [PATCH net-next v2 2/2] ptp: add FemtoClock3 Wireless as ptp hardware clock

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Date:   Thu, 30 Nov 2023 17:11:26 +0000
From:   Simon Horman <horms@...nel.org>
To:     Min Li <lnimi@...mail.com>
Cc:     richardcochran@...il.com, lee@...nel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Min Li <min.li.xe@...esas.com>
Subject: Re: [PATCH net-next v2 2/2] ptp: add FemtoClock3 Wireless as ptp
 hardware clock

On Wed, Nov 29, 2023 at 03:48:06PM -0500, Min Li wrote:
> From: Min Li <min.li.xe@...esas.com>
> 
> The RENESAS FemtoClock3 Wireless is a high-performance jitter attenuator,
> frequency translator, and clock synthesizer. The device is comprised of 3
> digital PLLs (DPLL) to track CLKIN inputs and three independent low phase
> noise fractional output dividers (FOD) that output low phase noise clocks.
> 
> FemtoClock3 supports one Time Synchronization (Time Sync) channel to enable
> an external processor to control the phase and frequency of the Time Sync
> channel and to take phase measurements using the TDC. Intended applications
> are synchronization using the precision time protocol (PTP) and
> synchronization with 0.5 Hz and 1 Hz signals from GNSS.
> 
> Signed-off-by: Min Li <min.li.xe@...esas.com>

Hi Min Li,

some minor feedback from my side.

...

> diff --git a/drivers/ptp/Makefile b/drivers/ptp/Makefile

...

> +static inline s64 ns2counters(struct idtfc3 *idtfc3, s64 nsec, u32 *sub_ns)
> +{
> +	s64 sync;
> +	s32 rem;
> +
> +	if (likely(nsec > 0)) {
> +		sync = div_u64_rem(nsec, idtfc3->ns_per_sync, &rem);
> +		*sub_ns = rem;
> +	} else if (nsec < 0) {
> +		sync = -div_u64_rem(-nsec - 1, idtfc3->ns_per_sync, &rem) - 1;
> +		*sub_ns = idtfc3->ns_per_sync - rem - 1;
> +	}
> +
> +	return sync * idtfc3->ns_per_sync;

Perhaps it cannot occur, but if nsec is exactly 0, then
sync is uninitialised here.

Flagged by clang-17 W=1 build, and Smatch.

> +}

...

> +static int _idtfc3_settime(struct idtfc3 *idtfc3, const struct timespec64 *ts)
> +{
> +	s64 offset_ns, now_ns, sync_ns;
> +	u32 counter, sub_ns;
> +	int now;
> +
> +	if (timespec64_valid(ts) == false) {
> +		dev_err(idtfc3->dev, "%s: invalid timespec", __func__);
> +		return -EINVAL;
> +	}
> +
> +	now = idtfc3_read_subcounter(idtfc3);
> +	if (now < 0)
> +		return now;
> +
> +	offset_ns = (idtfc3->sub_sync_count - now) * idtfc3->ns_per_counter;
> +	now_ns = timespec64_to_ns(ts);
> +	sync_ns = ns2counters(idtfc3, offset_ns + now_ns, &sub_ns);

sync_ns is set here but otherwise unused.
Perhaps the assignment can be dropped and sync_ns removed from this
function?

As flagged by gcc-13 W=1 build and Smatch.

> +
> +	counter = sub_ns / idtfc3->ns_per_counter;
> +	return idtfc3_timecounter_update(idtfc3, counter, now_ns);
> +}

...