From: Daniel Thompson <daniel.thompson@linaro.org>
To: Srinivas Kandagatla <srinivas.kandagatla@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, patches@linaro.org,
linaro-kernel@lists.linaro.org,
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: Re: [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel_relaxed()
Date: Tue, 09 Sep 2014 12:15:16 +0100 [thread overview]
Message-ID: <540EE144.8030504@linaro.org> (raw)
In-Reply-To: <CALNtEFgd=Lw3AdO2cq_X66_kVdjRyu8sVKN5UX3tzKS5c6d_JA@mail.gmail.com>
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
>
>
prev parent reply other threads:[~2014-09-09 11:15 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 ` [PATCH 3.17-rc3 v2] " Daniel Thompson
[not found] ` <CALNtEFgd=Lw3AdO2cq_X66_kVdjRyu8sVKN5UX3tzKS5c6d_JA@mail.gmail.com>
2014-09-09 11:15 ` Daniel Thompson [this message]
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