linux-kernel - [PATCH 15/24] tty: serial: fsl_lpuart: Use cpu

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Date:   Mon, 29 Jul 2019 12:52:17 -0700
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     linux-serial@...r.kernel.org
Cc:     Andrey Smirnov <andrew.smirnov@...il.com>,
        Stefan Agner <stefan@...er.ch>,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        Chris Healy <cphealy@...il.com>,
        Cory Tusar <cory.tusar@....aero>,
        Lucas Stach <l.stach@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-imx@....com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 15/24] tty: serial: fsl_lpuart: Use cpu_relax() instead of barrier()

Use cpu_relax() instead of barrier() in a tight polling loops to make
them a bit more idiomatic. Should also improve things on ARM64 a bit
since cpu_relax() will expand into "yield" instruction there.

Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
Cc: Stefan Agner <stefan@...er.ch>
Cc: Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
Cc: Chris Healy <cphealy@...il.com>
Cc: Cory Tusar <cory.tusar@....aero>
Cc: Lucas Stach <l.stach@...gutronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.com>
Cc: linux-imx@....com
Cc: linux-serial@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 drivers/tty/serial/fsl_lpuart.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index dde5caf724ff..7a0f96952291 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -552,14 +552,14 @@ static void lpuart_wait_bit_set(struct uart_port *port, unsigned int offset,
 				u8 bit)
 {
 	while (!(readb(port->membase + offset) & bit))
-		barrier();
+		cpu_relax();
 }
 
 static void lpuart32_wait_bit_set(struct uart_port *port, unsigned int offset,
 				  u32 bit)
 {
 	while (!(lpuart32_read(port, offset) & bit))
-		barrier();
+		cpu_relax();
 }
 
 #if defined(CONFIG_CONSOLE_POLL)
-- 
2.21.0