serial: zs: Convert to use a platform device

In the Linux kernel, the following vulnerability has been resolved:

serial: zs: Convert to use a platform device

Prevent a crash from happening as the first serial port is initialised:

Console: switching to mono frame buffer device 160x64

fb0: PMAG-AA frame buffer device at tc0

DECstation Z85C30 serial driver version 0.10

CPU 0 Unable to handle kernel paging request at virtual address 0000002c, epc == 803ab00c, ra == 803aafe0

Oops[#1]:

CPU: 0 PID: 1 Comm: swapper Not tainted 6.4.0-rc3-00031-g84a9582fd203-dirty #57

$ 0 : 00000000 10012c00 803aaeb0 00000000

$ 4 : 80e12f60 80e12f50 80e12f58 81000030

$ 8 : 00000000 805ff37c 00000000 33433538

$12 : 65732030 00000006 80c2915d 6c616972

$16 : 80e12f00 807b7630 00000000 00000000

$20 : 00000004 00000348 000001a0 807623b8

$24 : 00000018 00000000

$28 : 80c24000 80c25d60 8078b148 803aafe0

Hi : 00000000

Lo : 00000000

epc : 803ab00c serial_base_ctrl_add+0x78/0xf4

ra : 803aafe0 serial_base_ctrl_add+0x4c/0xf4

Status: 10012c03 KERNEL EXL IE

Cause : 00000008 (ExcCode 02)

BadVA : 0000002c

PrId : 00000440 (R4400SC)

Modules linked in:

Process swapper (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000)

Stack : 80760000 00000cc0 00400044 00400040 803aa02c 80d61ab8 00000000 807b7630

80760000 807623b8 807b7628 803aa644 80386998 00000000 80e17780 80220f68

80e17780 80d61ab8 80c17d80 80e17780 80e17780 8063c798 80e17780 80383fa0

00000010 80e17780 00000000 80386998 807a0000 00000000 00400040 8038f848

807623b8 80d61ab8 00000004 80e17780 00000000 803a68e4 80c25e2c 803bb884

...

Call Trace:

[<803ab00c>] serial_base_ctrl_add+0x78/0xf4

[<803aa644>] serial_core_register_port+0x174/0x69c

[<8077e9ac>] zs_init+0xc8/0xfc

[<800404d4>] do_one_initcall+0x40/0x2ac

[<8076cecc>] kernel_init_freeable+0x1e4/0x270

[<80605bec>] kernel_init+0x20/0x108

[<800431e8>] ret_from_kernel_thread+0x14/0x1c

Code: 2442aeb0 ae120024 ae0200d0 <8c67002c> 50e00001 8c670000 3c06806e 3c05806e afb30010

---[ end trace 0000000000000000 ]---

(report at the offending commit) -- where a pointer is dereferenced that

has been derived from a null pointer to the port's parent device.

Since no device is available with legacy probing and it's not anymore a

preferable way to discover devices anyway, switch the driver to using a

platform device and use it as the port's parent device. Update resource

handling accordingly and only request the actual span of addresses used

within the slot, which will have had its resource already requested by

generic platform device code.

Use platform_driver_probe() not just because SCC devices are fixed with

solder on board and not straightforward to remove, but foremost because

the associated TTY's major device number is the same as used by the dz

driver and the first driver to claim it will prevent the other one from

using it. Either one DZ device or some SCC devices will be present in a

given system but never both at a time, and therefore we want the major

device number to be claimed by the first driver to actually successfully

bind to its device and platform_driver_probe() is a way to fulfil that.

An unfortunate consequence of the switch to a platform device is we now

hand the console over from the bootconsole much later in the bootstrap.

The firmware console handler appears good enough though to work so late

and in particular with interrupts enabled.

Since there is one way only remaining to reach zs_reset() now, remove

the port initialisation marker as no longer needed and go through the

channel reset unconditionally.