The architectures supported by this driver 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 driver is cross compilable for testing purposes and remains compilable on all architectures by falling back to writel() when writel_relaxed() does not exist. We also include explicit compiler barriers. There are redundant on ARM and SH but important on x86 because it defines "relaxed" differently.
Signed-off-by: Daniel Thompson daniel.thompson@linaro.org Cc: Srinivas Kandagatla srinivas.kandagatla@gmail.com Cc: Maxime Coquelin maxime.coquelin@st.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 --- drivers/tty/serial/st-asc.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c index 4f376d8..58aa1c6 100644 --- a/drivers/tty/serial/st-asc.c +++ b/drivers/tty/serial/st-asc.c @@ -152,12 +152,21 @@ 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); + u32 r; + + r = readl_relaxed(port->membase + offset); + barrier(); + return r; }
static inline void asc_out(struct uart_port *port, u32 offset, u32 value) { +#ifdef writel_relaxed + writel_relaxed(value, port->membase + offset); + barrier(); +#else writel(value, port->membase + offset); +#endif }
/*