netdev - Re: [PATCH RESEND net-next v2] net: stmmac: dwmac: Add a fixup for the Micrel KSZ9131 PHY

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Message-ID: <aWJ0iV6-_4XqpeHD@shell.armlinux.org.uk>
Date: Sat, 10 Jan 2026 15:47:21 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Stefan Eichenberger <eichest@...il.com>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Andrew Lunn <andrew@...n.ch>, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, shawnguo@...nel.org, s.hauer@...gutronix.de,
	kernel@...gutronix.de, festevam@...il.com,
	mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
	linux-stm32@...md-mailman.stormreply.com, netdev@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, francesco.dolcini@...adex.com,
	robh@...nel.org,
	Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH RESEND net-next v2] net: stmmac: dwmac: Add a fixup for
 the Micrel KSZ9131 PHY

On Sat, Jan 10, 2026 at 02:42:13PM +0100, Stefan Eichenberger wrote:
> Hi Maxime,
> 
> Not problem, thanks a lot for the feedback and the discussion. I will
> then proceed with the current approach and send a new version with an
> updated commit message.

We could add a flag to:

/* Generic phy_device::dev_flags */
#define PHY_F_NO_IRQ            0x80000000
#define PHY_F_RXC_ALWAYS_ON     0x40000000

indicating that the MAC requires the full preamble, which the PHY can
then test for and configure appropiately.

The question is, whether the requirement for the full preamble applies
to many MACs, and whether there are PHYs that default to producing
short preambles.

Looking at Marvell 88e151x, the only control it has is to pad odd
nibbles of preambles on copper (page 2, register 16, bit 6.)

AR8035 seems to make no mention of preamble for the MII interfaces, so
I guess it has no control over it.

I've not looked further than that.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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