serial: dz: Convert to use a platform device

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

serial: dz: Convert to use a platform device

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

Console: switching to colour frame buffer device 160x64

tgafb: SFB+ detected, rev=0x02

fb0: Digital ZLX-E1 frame buffer device at 0x1e000000

DECstation DZ serial driver version 1.04

CPU 0 Unable to handle kernel paging request at virtual address 000000bc, epc == 8048b3a4, ra == 80470a78

Oops[#1]:

CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0-dirty #35 NONE

$ 0 : 00000000 1000ac00 00000004 804707ac

$ 4 : 00000000 80e20850 80e20858 81000030

$ 8 : 00000000 8072c81c 00000008 fefefeff

$12 : 6c616972 00000006 80c5917f 69726420

$16 : 80e20800 00000000 808f8968 80e20800

$20 : 00000000 807f5a90 808b0094 808d3bc8

$24 : 00000018 80479030

$28 : 80c2e000 80c2fd70 00000069 80470a78

Hi : 00000004

Lo : 00000000

epc : 8048b3a4 __dev_fwnode+0x0/0xc

ra : 80470a78 serial_base_ctrl_add+0xa0/0x168

Status: 1000ac04 IEp

Cause : 30000008 (ExcCode 02)

BadVA : 000000bc

PrId : 00000220 (R3000)

Modules linked in:

Process swapper/0 (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000)

Stack : 00400044 00400040 8046f4cc 00000000 808a6148 808a0000 808f8968 8086983c

808e0000 8046fc84 1000ac01 00000028 80e20700 802ba3f8 80e20700 80d34a94

80c1b900 80e20700 80e20700 80e20700 80e20700 80444650 00000000 00000000

00000000 807f5a90 808b0094 80447080 00400040 808e0000 80d34a94 808a6148

80d34a94 00000004 80e20700 00000000 8076974c 80469810 80c2fe3c 1000ac01

...

Call Trace:

[<8048b3a4>] __dev_fwnode+0x0/0xc

[<80470a78>] serial_base_ctrl_add+0xa0/0x168

[<8046fc84>] serial_core_register_port+0x1c8/0x974

[<808c6af0>] dz_init+0x74/0xc8

[<800470e0>] do_one_initcall+0x44/0x2d4

[<808b111c>] kernel_init_freeable+0x258/0x308

[<8072e434>] kernel_init+0x20/0x114

[<80049cd0>] ret_from_kernel_thread+0x14/0x1c

Code: 27bd0018 03e00008 2402ffea <8c8200bc> 03e00008 00000000 27bdffc0 afbe0038 afb30024

---[ end trace 0000000000000000 ]---

-- 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 the DZ device is 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 zs

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.

Conversely only starting the console port so late lets the reset code

fully utilise our delay handlers, so switch from udelay() to fsleep()

for transmitter draining so as to avoid busy-waiting for an excessive

amount of time.