tty: Add SBI debug console support to HVC SBI driver

RISC-V SBI specification supports advanced debug console
support via SBI DBCN extension.

Extend the HVC SBI driver to support it.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20231124070905.1043092-5-apatel@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

tty: hvc: convert to u8 and size_t

Switch character types to u8 and sizes to size_t. To conform to
characters/sizes in the rest of the tty layer.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Amit Shah <amit@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: virtualization@lists.linux.dev
Cc: linux-riscv@lists.infradead.org
Link: https://lore.kernel.org/r/20231206073712.17776-13-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty: Don't force RISCV SBI console as preferred console

The Linux kernel will auto-disables all boot consoles whenever it
gets a preferred real console.

Currently on RISC-V systems, if we have a real console which is not
RISCV SBI console then boot consoles (such as earlycon=sbi) are not
auto-disabled when a real console (ttyS0 or ttySIF0) is available.
This results in duplicate prints at boot-time after kernel starts
using real console (i.e. ttyS0 or ttySIF0) if "earlycon=" kernel
parameter was passed by bootloader.

The reason for above issue is that RISCV SBI console always adds
itself as preferred console which is causing other real consoles
to be not used as preferred console.

Ideally "console=" kernel parameter passed by bootloaders should
be the one selecting a preferred real console.

This patch fixes above issue by not forcing RISCV SBI console as
preferred console.

Fixes: afa6b1ccfad5 ("tty: New RISC-V SBI console driver")
Cc: stable@vger.kernel.org
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

tty: New RISC-V SBI console driver

The RISC-V ISA defines a simple console that is availiable via SBI calls
on all systems. The SBI console is designed to be availiable at all
times, so while it's most natural to use this as an early printk target
it's also possible to use this as the system console when there isn't a
better one availiable.

This patch adds support for the RISC-V SBI console via the HVC
infastructure. It's entirely independent from our early printk support,
which results in early boot messages appearing twice over the SBI
console. As far as I can tell that's the fault of our early printk
support (we should support earlycon) as opposed to this driver.

There is one checkpatch.pl warning here: to check the MAINTAINERS file.
They're all matched by the "K: riscv" line.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>