netdev - Re: [PATCH RFC] net: mdio_bus: make check in mdiobus_prevent_c45

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Message-ID: <ZZQpK9Uw72qhxA6l@shell.armlinux.org.uk>
Date: Tue, 2 Jan 2024 15:18:03 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC] net: mdio_bus: make check in
 mdiobus_prevent_c45_scan more granular

On Tue, Jan 02, 2024 at 03:38:05PM +0100, Heiner Kallweit wrote:
> Matching on OUI level is a quite big hammer. So let's make matching
> more granular.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
> This is what I'm thinking of. Maybe the problem of misbehaving
> on c45 access affects certain groups of PHY's only.
> Then we don't have to blacklist all PHY's from this vendor.
> What do you think?
> ---
>  drivers/net/phy/mdio_bus.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index 6cf73c156..848d5d2d6 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -621,19 +621,27 @@ static int mdiobus_scan_bus_c45(struct mii_bus *bus)
>   */
>  static bool mdiobus_prevent_c45_scan(struct mii_bus *bus)
>  {
> -	int i;
> +	const struct {
> +		u32 phy_id;
> +		u32 phy_id_mask;
> +	} id_list[] = {
> +		{ MICREL_OUI << 10, GENMASK(31, 10) },
> +	};

Do we need a new structure? Would struct mdio_device_id do (which
actually has exactly the same members with exactly the same names in
exactly the same order.)

Also, as this is not static, the compiler will need to generate code
to initialise the structure, possibly storing a copy of it in the
.data segment and memcpy()ing it onto the kernel stack. I suggest
marking it static to avoid that unnecessary hidden code complexity.

> +		for (j = 0; j < ARRAY_SIZE(id_list); j++) {
> +			u32 mask = id_list[j].phy_id_mask;
> +
> +			if ((phydev->phy_id & mask) == (id_list[j].phy_id & mask))

			if (phy_id_compare(phydev->phy_id, id_list[j].phy_id,
					   id_list[j].phy_id_mask))

Or it could be:

			const struct mdio_device_id *id = id_list + j;

			if (phy_id_compare(phydev->phy_id, id->phy_id,
					   id->phy_id_mask))

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