netdev - Re: [PATCH v2 net-next] net: phy: add basic driver for NXP CBTX PHY

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Date:   Fri, 21 Apr 2023 14:07:24 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH v2 net-next] net: phy: add basic driver for NXP CBTX PHY

On Tue, Apr 18, 2023 at 10:01:41PM +0300, Vladimir Oltean wrote:
> The CBTX PHY is a Fast Ethernet PHY integrated into the SJA1110 A/B/C
> automotive Ethernet switches.
> 
> It was hoped it would work with the Generic PHY driver, but alas, it
> doesn't. The most important reason why is that the PHY is powered down
> by default, and it needs a vendor register to power it on.
> 
> It has a linear memory map that is accessed over SPI by the SJA1110
> switch driver, which exposes a fake MDIO controller. It has the
> following (and only the following) standard clause 22 registers:
> 
> 0x0: MII_BMCR
> 0x1: MII_BMSR
> 0x2: MII_PHYSID1
> 0x3: MII_PHYSID2
> 0x4: MII_ADVERTISE
> 0x5: MII_LPA
> 0x6: MII_EXPANSION
> 0x7: the missing MII_NPAGE for Next Page Transmit Register
> 
> Every other register is vendor-defined.
> 
> The register map expands the standard clause 22 5-bit address space of
> 0x20 registers, however the driver does not need to access the extra
> registers for now (and hopefully never). If it ever needs to do that, it
> is possible to implement a fake (software) page switching mechanism
> between the PHY driver and the SJA1110 MDIO controller driver.
> 
> Also, Auto-MDIX is turned off by default in hardware, the driver turns
> it on by default and reports the current status. I've tested this with a
> VSC8514 link partner and a crossover cable, by forcing the mode on the
> link partner, and seeing that the CBTX PHY always sees the reverse of
> the mode forced on the VSC8514 (and that traffic works). The link
> doesn't come up (as expected) if MDI modes are forced on both ends in
> the same way (with the cross-over cable, that is).
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew