netdev - Re: [Intel-wired-lan] [PATCH v10 iwl-next 05/11] idpf: negotiate PTP capabilities and get PTP clock

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Message-ID: <fd2098e1-c5c5-4cf8-b34e-ebe0bd288248@intel.com>
Date: Tue, 8 Apr 2025 14:15:21 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Milena Olech <milena.olech@...el.com>, <intel-wired-lan@...ts.osuosl.org>
CC: <netdev@...r.kernel.org>, <anthony.l.nguyen@...el.com>,
	<przemyslaw.kitszel@...el.com>, Willem de Bruijn <willemb@...gle.com>, "Mina
 Almasry" <almasrymina@...gle.com>, Samuel Salin <Samuel.salin@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH v10 iwl-next 05/11] idpf: negotiate PTP
 capabilities and get PTP clock



On 4/8/2025 3:30 AM, Milena Olech wrote:
> +static u64 idpf_ptp_read_src_clk_reg_direct(struct idpf_adapter *adapter,
> +					    struct ptp_system_timestamp *sts)
> +{
> +	struct idpf_ptp *ptp = adapter->ptp;
> +	u32 hi, lo;
> +
> +	spin_lock(&ptp->read_dev_clk_lock);
> +
> +	/* Read the system timestamp pre PHC read */
> +	ptp_read_system_prets(sts);
> +
> +	idpf_ptp_enable_shtime(adapter);
> +
> +	/* Read the system timestamp post PHC read */
> +	ptp_read_system_postts(sts);
> +
> +	lo = readl(ptp->dev_clk_regs.dev_clk_ns_l);
> +	hi = readl(ptp->dev_clk_regs.dev_clk_ns_h);
> +
> +	spin_unlock(&ptp->read_dev_clk_lock);
> +
> +	return ((u64)hi << 32) | lo;
> +}
v9 had comments regarding the latching of the registers for direct
access. Can you confirm whether this is known to be safe, or if you need
to implement a 3-part read like we do in ice and other hardware? Even
with a spinlock there could be issues with rollover in the hardware I think?

Thanks,
Jake