linux-kernel - [PATCH v5 4/5] serial: 8250: Export ICR access helpers for internal use

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Date:   Mon, 18 Apr 2022 16:27:27 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v5 4/5] 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@...am.me.uk>
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
---
Changes from v4:

- Reorder as 4/5 (from 3/5).

- Drop `__maybe_unused' from `serial_icr_write'; it's used by 
  `serial_icr_read'.

New change in v4, factored out from 5/5.
---
 drivers/tty/serial/8250/8250.h      |   22 ++++++++++++++++++++++
 drivers/tty/serial/8250/8250_port.c |   21 ---------------------
 2 files changed, 22 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 +120,28 @@ static inline void serial_out(struct uar
 	up->port.serial_out(&up->port, offset, value);
 }
 
+/*
+ * 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 __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)