linux-kernel - [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel

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Date:	Tue,  9 Sep 2014 11:03:57 +0100
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	linux-kernel@...r.kernel.org, patches@...aro.org,
	linaro-kernel@...ts.linaro.org,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Patrice Chotard <patrice.chotard@...com>,
	Jiri Slaby <jslaby@...e.cz>, kernel@...inux.com,
	linux-serial@...r.kernel.org
Subject: [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel_relaxed()

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@...aro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@...il.com>
Cc: Maxime Coquelin <maxime.coquelin@...com>
Cc: Patrice Chotard <patrice.chotard@...com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: kernel@...inux.com
Cc: linux-serial@...r.kernel.org
---

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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