net: dsa: microchip: properly support platform_data probing

net: dsa: microchip: properly support platform_data probing

The ksz driver has bits and pieces of platform_data probing support, but
it doesn't work.

The conventional thing to do is to have an encapsulating structure for
struct dsa_chip_data that gets put into dev->platform_data. This driver
expects a struct ksz_platform_data, but that doesn't contain a struct
dsa_chip_data as first element, which will obviously not work with
dsa_switch_probe() -> dsa_switch_parse().

Pointing dev->platform_data to a struct dsa_chip_data directly is in
principle possible, but that doesn't work either. The driver has
ksz_switch_detect() to read the device ID from hardware, followed by
ksz_check_device_id() to compare it against a predetermined expected
value. This protects against early errors in the SPI/I2C communication.
With platform_data, the mechanism in ksz_check_device_id() doesn't work
and even leads to NULL pointer dereferences, since of_device_get_match_data()
doesn't work in that probe path.

So obviously, the platform_data support is actually missing, and the
existing handling of struct ksz_platform_data is bogus. Complete the
support by adding a struct dsa_chip_data as first element, and fixing up
ksz_check_device_id() to pick up the platform_data instead of the
unavailable of_device_get_match_data().

The early dev->chip_id assignment from ksz_switch_register() is also
bogus, because ksz_switch_detect() sets it to an initial value. So
remove it.

Also, ksz_platform_data :: enabled_ports isn't used anywhere, delete it.

Link: https://lore.kernel.org/netdev/20231204154315.3906267-1-dd@embedd.com/
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Daniel Danzberger <dd@embedd.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>