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@linaro.org Cc: Srinivas Kandagatla srinivas.kandagatla@gmail.com Cc: Patrice Chotard patrice.chotard@st.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.cz Cc: kernel@stlinux.com Cc: linux-serial@vger.kernel.org Acked-by: Maxime Coquelin maxime.coquelin@st.com Acked-by: Peter Griffin peter.griffin@linaro.org --- 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 config SERIAL_ST_ASC tristate "ST ASC serial port support" select SERIAL_CORE - depends on ARM || COMPILE_TEST + depends on ARM help 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); }
/* -- 1.9.3