9 Sep
2014
9 Sep
'14
11:15 a.m.
On 09/09/14 12:08, Srinivas Kandagatla wrote:
Hi Dan,
After Greg's comment, Am ok with the patch and sorry for the noise. Good that you removed the barier() too.
Yes.
I got interested in Greg's question about which architectures don't have readl_relaxed() and, in the process, discovered I was wrong about that being needed anyway.
You can have my Ack.
--srini
On Tue, Sep 9, 2014 at 11:03 AM, Daniel Thompson <daniel.thompson@linaro.org mailto:daniel.thompson@linaro.org> wrote:
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@linaro.org <mailto:daniel.thompson@linaro.org>> Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.com <mailto:srinivas.kandagatla@gmail.com>> Cc: Maxime Coquelin <maxime.coquelin@st.com <mailto:maxime.coquelin@st.com>> Cc: Patrice Chotard <patrice.chotard@st.com <mailto:patrice.chotard@st.com>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org <mailto:gregkh@linuxfoundation.org>> Cc: Jiri Slaby <jslaby@suse.cz <mailto:jslaby@suse.cz>> Cc: kernel@stlinux.com <mailto:kernel@stlinux.com> Cc: linux-serial@vger.kernel.org <mailto:linux-serial@vger.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