linux-kernel - Re: [PATCH net-next v5 3/4] net: phy: Allow pre-declaration of MDIO devices

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Date:   Mon, 6 Feb 2017 15:04:43 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, Jason Cooper <jason@...edaemon.net>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Russell King <linux@...linux.org.uk>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        "David S. Miller" <davem@...emloft.net>,
        "moderated list:ARM/Marvell Dove/MV78xx0/Orion SOC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v5 3/4] net: phy: Allow pre-declaration of MDIO
 devices

> +/**
> + * mdio_register_board_info - register MDIO devices for a given board
> + * @info: array of devices descriptors
> + * @n: number of descriptors provided
> + * Context: can sleep
> + *
> + * The board info passed can be marked with __initdata but be pointers
> + * such as platform_data etc. are copied as-is
> + */
> +int mdiobus_register_board_info(const struct mdio_board_info *info,
> +				unsigned int n)
> +{
> +	struct mdio_board_entry *be;
> +	unsigned int i;
> +
> +	be = kcalloc(n, sizeof(*be), GFP_KERNEL);
> +	if (!be)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < n; i++, be++, info++) {
> +		memcpy(&be->board_info, info, sizeof(*info));
> +		mutex_lock(&mdio_board_lock);
> +		list_add_tail(&be->list, &mdio_board_list);
> +		mutex_unlock(&mdio_board_lock);
> +	}
> +
> +	return 0;

Hi Florian

I've recently been playing with a hot-pluggable SPI bus controller. It
is a USB device, hence can come and go. On the SPI bus i have an
SRAM. On order to instantiate the MTD device, i need SPI board info. I
cannot add the board info until after the SPI bus master appears,
since i need to know its ID to fill in the board info. At the moment,
i have udev script which when the SPI bus master appears loads a
little kernel module which registers the board info.

Such a scheme will not work here. You need to iterate the list of MDIO
devices at the end of mdiobus_register_board_info() to see if the just
registered board info applies to any existing MDIO bus.

I don't think we yet have any hardware which would do this. But there
have been patches to one of the USB-Ethernet dongles to allow it run
without a PHY. My guess is, to allow an SFP module. But it is not too
big a step for somebody to make a USB attached Ethernet switch.

Maybe consider adding this functionality? Also an unregister call?

      Andrew