netdev - Re: [PATCH RFC net-next 03/20] net: phy: marvell: add PHY PTP support

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Message-ID: <299f61cc-b5a7-48a6-b16d-f1f5d639af85@lunn.ch>
Date: Thu, 18 Sep 2025 22:12:02 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Russell King <rmk+kernel@...linux.org.uk>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH RFC net-next 03/20] net: phy: marvell: add PHY PTP support

> +static u64 marvell_phy_tai_clock_read(struct device *dev,
> +				      struct ptp_system_timestamp *sts)
> +{
> +	struct phy_device *phydev = to_phy_device(dev);
> +	int err, oldpage, lo, hi;
> +
> +	oldpage = phy_select_page(phydev, MARVELL_PAGE_PTP_GLOBAL);
> +	if (oldpage >= 0) {
> +		/* 88e151x says to write 0x8e0e */
> +		ptp_read_system_prets(sts);
> +		err = __phy_write(phydev, PTPG_READPLUS_COMMAND, 0x8e0e);
> +		ptp_read_system_postts(sts);
> +		lo = __phy_read(phydev, PTPG_READPLUS_DATA);
> +		hi = __phy_read(phydev, PTPG_READPLUS_DATA);
> +	}
> +	err = phy_restore_page(phydev, oldpage, err);
> +
> +	if (err || lo < 0 || hi < 0)
> +		return 0;
> +
> +	return lo | hi << 16;

What happens when hi is >= 0x8000? Doesn't that result in undefined
behaviour for 32 bit machines? The u64 result we are trying to return
is big enough to hold the value. Does the hi need promoting to u64
before doing the shift?

       Andrew