Re: [PATCH net-next v4 2/3] ptp: Add driver for R-Car Gen4

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 02/07/2026 13:55, Niklas Söderlund wrote:
> Add driver for the gPTP timer found on R-Car Gen4 devices. The timer is
> system-wide and shared by different Ethernet devices on each Gen4
> platform. The operation of the timer is however not completely in
> depended of the systems Ethernet devices.
> 
>    - On R-Car S4 is gated by the RSWITCH Ethernet module clock.
> 
>    - On R-Car V4H is gated by the RTSN Ethernet module clock.
> 
>    - On R-Car V4M is gated by its own module clock, the system have
>      neither RTSN or RSWITCH device. But the module clock is the same as
>      RTSN on V4H and the documentation referees to it as tsn (EtherTSN).
> 
> The gPTP device do have its own register space on all three platforms.
> But on S4 and V4H it will share its clock and reset property with
> RSWITCH or RTSN, respectively.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> ---
> * Changes since v3
> - Clamp increment calculated to register limitations.
> - Check return value of clk_get_rate().
> - Disable PM if ptp_clock_register() fails.
> ---

[...]

> +struct ptp_rcar_gen4_priv {
> +	void __iomem *base;
> +	struct clk *clk;
> +
> +	struct ptp_clock *clock;
> +	struct ptp_clock_info info;
> +
> +	spinlock_t lock;	/* Registers access. */
> +	s64 default_addend;
> +};
> +
> +#define ptp_to_priv(ptp) container_of(ptp, struct ptp_rcar_gen4_priv, info)
> +
> +static int ptp_rcar_gen4_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
> +{
> +	struct ptp_rcar_gen4_priv *priv = ptp_to_priv(ptp);
> +	s64 addend = priv->default_addend;
> +	bool neg_adj = scaled_ppm < 0;
> +	unsigned long flags;
> +	s64 diff;
> +
> +	if (neg_adj)
> +		scaled_ppm = -scaled_ppm;
> +	diff = div_s64(addend * scaled_ppm_to_ppb(scaled_ppm), NSEC_PER_SEC);
> +	addend = neg_adj ? addend - diff : addend + diff;
> +
> +	/* Clamp value to register limits, defined as in nanoseconds.
> +	 * bit[31:27] - integer
> +	 * bit[26:0]  - decimal
> +	 */
> +	addend = clamp_val(addend, 0, UINT_MAX);

is it always positive number?

> +
> +	spin_lock_irqsave(&priv->lock, flags);
> +	iowrite32(addend, priv->base + PTPTIVC0_REG);
> +	spin_unlock_irqrestore(&priv->lock, flags);
> +
> +	return 0;
> +}

[...]

> +static struct ptp_clock_info ptp_rcar_gen4_info = {
> +	.owner = THIS_MODULE,
> +	.name = "R-Car Gen4 gPTP",
> +	.max_adj = 50000000,

even though clamping addend may work, I would suggest adjusting
".max_adj" value to the one which will not make addend overflow.
And as a reminder, .max_adj is the absolute value in ppb that can be set
for a single call of .adjfine - the value is checked against
[-(.max_adj),.max_adj] range.

> +	.adjfine = ptp_rcar_gen4_adjfine,
> +	.adjtime = ptp_rcar_gen4_adjtime,
> +	.gettime64 = ptp_rcar_gen4_gettime,
> +	.settime64 = ptp_rcar_gen4_settime,
> +};