linux-kernel - Re: [PATCH v4 3/5] serial: 8250: Export ICR access helpers for internal use

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Date:   Mon, 18 Apr 2022 15:17:38 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] serial: 8250: Export ICR access helpers for
 internal use

On Mon, Apr 18, 2022 at 2:02 AM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
> 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.

Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
See one nit-pick below.

> Signed-off-by: Maciej W. Rozycki <macro@...am.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
> 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.

> +{
> +       serial_out(up, UART_SCR, offset);
> +       serial_out(up, UART_ICR, value);
> +}
> +
> +static unsigned int __maybe_unused serial_icr_read(struct uart_8250_port *up,
> +                                                  int offset)
> +{
> +       unsigned int value;
> +
> +       serial_icr_write(up, UART_ACR, up->acr | UART_ACR_ICRRD);
> +       serial_out(up, UART_SCR, offset);
> +       value = serial_in(up, UART_ICR);
> +       serial_icr_write(up, UART_ACR, up->acr);
> +
> +       return value;
> +}
> +
>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p);
>
>  static inline int serial_dl_read(struct uart_8250_port *up)
> Index: linux-macro/drivers/tty/serial/8250/8250_port.c
> ===================================================================
> --- linux-macro.orig/drivers/tty/serial/8250/8250_port.c
> +++ linux-macro/drivers/tty/serial/8250/8250_port.c
> @@ -538,27 +538,6 @@ serial_port_out_sync(struct uart_port *p
>  }
>
>  /*
> - * For the 16C950
> - */
> -static void serial_icr_write(struct uart_8250_port *up, int offset, int value)
> -{
> -       serial_out(up, UART_SCR, offset);
> -       serial_out(up, UART_ICR, value);
> -}
> -
> -static unsigned int serial_icr_read(struct uart_8250_port *up, int offset)
> -{
> -       unsigned int value;
> -
> -       serial_icr_write(up, UART_ACR, up->acr | UART_ACR_ICRRD);
> -       serial_out(up, UART_SCR, offset);
> -       value = serial_in(up, UART_ICR);
> -       serial_icr_write(up, UART_ACR, up->acr);
> -
> -       return value;
> -}
> -
> -/*
>   * FIFO support.
>   */
>  static void serial8250_clear_fifos(struct uart_8250_port *p)



-- 
With Best Regards,
Andy Shevchenko