[PATCH 3.17-rc3] serial: asc: Adopt readl_/writel_relaxed()

From: Daniel Thompson
Date: Wed Sep 03 2014 - 08:01:13 EST

The architectures where this peripheral exists (ARM and SH) have expensive
implementations of writel(), reliant on spin locks and explicit L2 cache
management. These architectures provide a cheaper writel_relaxed() which
is much better suited to peripherals that do not perform DMA. The
situation with readl()/readl_relaxed()is similar although less acute.

This driver does not use DMA and will be more power efficient and more
robust (due to absense of spin locks during console I/O) if it uses the
relaxed variants.

This change means the driver is no longer portable and therefore no
longer suitable for compile testing.

Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxx>
Cc: Patrice Chotard <patrice.chotard@xxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: kernel@xxxxxxxxxxx
Cc: linux-serial@xxxxxxxxxxxxxxx
Acked-by: Maxime Coquelin <maxime.coquelin@xxxxxx>
Acked-by: Peter Griffin <peter.griffin@xxxxxxxxxx>
drivers/tty/serial/Kconfig | 2 +-
drivers/tty/serial/st-asc.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 26cec64d..e9b1735 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1527,7 +1527,7 @@ config SERIAL_FSL_LPUART_CONSOLE
tristate "ST ASC serial port support"
- depends on ARM || COMPILE_TEST
+ depends on ARM
This driver is for the on-chip Asychronous Serial Controller on
STMicroelectronics STi SoCs.
diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
index 8b2d735..adadbc1 100644
--- a/drivers/tty/serial/st-asc.c
+++ b/drivers/tty/serial/st-asc.c
@@ -151,12 +151,12 @@ static inline struct asc_port *to_asc_port(struct uart_port *port)

static inline u32 asc_in(struct uart_port *port, u32 offset)
- return readl(port->membase + offset);
+ return readl_relaxed(port->membase + offset);

static inline void asc_out(struct uart_port *port, u32 offset, u32 value)
- writel(value, port->membase + offset);
+ writel_relaxed(value, port->membase + offset);


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