From: Daniel Thompson <daniel.thompson@linaro.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>,
linux-kernel@vger.kernel.org, patches@linaro.org,
linaro-kernel@lists.linaro.org,
Srinivas Kandagatla <srinivas.kandagatla@gmail.com>,
Maxime Coquelin <maxime.coquelin@st.com>,
Patrice Chotard <patrice.chotard@st.com>,
Jiri Slaby <jslaby@suse.cz>,
kernel@stlinux.com, linux-serial@vger.kernel.org
Subject: [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel_relaxed()
Date: Tue, 9 Sep 2014 11:03:57 +0100 [thread overview]
Message-ID: <1410257037-20030-1-git-send-email-daniel.thompson@linaro.org> (raw)
In-Reply-To: <1409745651-3247-1-git-send-email-daniel.thompson@linaro.org>
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>
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
---
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
next prev parent reply other threads:[~2014-09-09 10:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-03 12:00 [PATCH 3.17-rc3] serial: asc: Adopt readl_/writel_relaxed() Daniel Thompson
2014-09-08 23:27 ` Greg Kroah-Hartman
2014-09-09 9:38 ` Daniel Thompson
2014-09-09 10:03 ` Daniel Thompson [this message]
[not found] ` <CALNtEFgd=Lw3AdO2cq_X66_kVdjRyu8sVKN5UX3tzKS5c6d_JA@mail.gmail.com>
2014-09-09 11:15 ` [PATCH 3.17-rc3 v2] " Daniel Thompson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1410257037-20030-1-git-send-email-daniel.thompson@linaro.org \
--to=daniel.thompson@linaro.org \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.cz \
--cc=kernel@stlinux.com \
--cc=linaro-kernel@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-serial@vger.kernel.org \
--cc=maxime.coquelin@st.com \
--cc=patches@linaro.org \
--cc=patrice.chotard@st.com \
--cc=srinivas.kandagatla@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).