The architectures supported by this driver, 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 absence of spin locks during console I/O) if it uses the
relaxed variants.
The driver supports COMPILE_TEST and therefore falls back to writel()
when writel_relaxed() does not exist.
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxx>
Cc: Maxime Coquelin <maxime.coquelin@xxxxxx>
Cc: Patrice Chotard <patrice.chotard@xxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: kernel@xxxxxxxxxxx
Cc: linux-serial@xxxxxxxxxxxxxxx
---
Notes:
Changes since v1:
* Added fallback to writel() to permit COMPILE_TESTing (review
of Greg Kroah-Hartmam).
drivers/tty/serial/st-asc.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
index 8b2d735..a3fc167 100644
--- a/drivers/tty/serial/st-asc.c
+++ b/drivers/tty/serial/st-asc.c
@@ -151,12 +151,16 @@ 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)
{
+#ifdef writel_relaxed
+ writel_relaxed(value, port->membase + offset);
+#else
writel(value, port->membase + offset);
+#endif
}
/*
--
1.9.3
--
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