[v4,3/5] serial: 8250: Export ICR access helpers for internal use

Make ICR access helpers available outside 8250_port.c, however retain 
them as ordinary static functions so as not to regress code generation.

This is because `serial_icr_write' is currently automatically inlined by 
GCC, however `serial_icr_read' is not.  Making them both static inline 
would grow code produced, e.g.:

$ i386-linux-gnu-size --format=gnu 8250_port-{old,new}.o
      text       data        bss      total filename
     15065       3378          0      18443 8250_port-old.o
     15289       3378          0      18667 8250_port-new.o

and:

$ riscv64-linux-gnu-size --format=gnu 8250_port-{old,new}.o
      text       data        bss      total filename
     16980       5306          0      22286 8250_port-old.o
     17124       5306          0      22430 8250_port-new.o

while making them external would needlessly add a new module interface 
and lose the benefit from `serial_icr_write' getting inlined outside 
8250_port.o.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
---
New change in v4, factored out from 5/5.
---
 drivers/tty/serial/8250/8250.h      |   23 +++++++++++++++++++++++
 drivers/tty/serial/8250/8250_port.c |   21 ---------------------
 2 files changed, 23 insertions(+), 21 deletions(-)

linux-serial-8250-icr-access.diff

On Mon, 18 Apr 2022, Andy Shevchenko wrote:

> > Index: linux-macro/drivers/tty/serial/8250/8250.h
> > ===================================================================
> > --- linux-macro.orig/drivers/tty/serial/8250/8250.h
> > +++ linux-macro/drivers/tty/serial/8250/8250.h
> > @@ -120,6 +120,29 @@ static inline void serial_out(struct uar
> >         up->port.serial_out(&up->port, offset, value);
> >  }
> >
> > +/*
> > + * For the 16C950
> > + */
> > +static void __maybe_unused serial_icr_write(struct uart_8250_port *up,
> > +                                           int offset, int value)
> 
> I think you may drop __maybe_unused here, because it's always used by
> the code below. So it will be eliminated altogether when the below
> won't be used.

 Right, the absence of this annotation doesn't cause GCC to complain about 
sources that define this function but do not make use of it, so I have 
removed the atttribute in v5.

  Maciej