* [PATCH 3.17-rc3] serial: asc: Adopt readl_/writel_relaxed()
@ 2014-09-03 12:00 Daniel Thompson
2014-09-08 23:27 ` Greg Kroah-Hartman
2014-09-09 10:03 ` [PATCH 3.17-rc3 v2] " Daniel Thompson
0 siblings, 2 replies; 5+ messages in thread
From: Daniel Thompson @ 2014-09-03 12:00 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Daniel Thompson, linux-kernel, patches, linaro-kernel,
Srinivas Kandagatla, Patrice Chotard, Jiri Slaby, kernel,
linux-serial
The architectures where this peripheral exists (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 absense of spin locks during console I/O) if it uses the
relaxed variants.
This change means the driver is no longer portable and therefore no
longer suitable for compile testing.
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.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
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
---
drivers/tty/serial/Kconfig | 2 +-
drivers/tty/serial/st-asc.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 26cec64d..e9b1735 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1527,7 +1527,7 @@ config SERIAL_FSL_LPUART_CONSOLE
config SERIAL_ST_ASC
tristate "ST ASC serial port support"
select SERIAL_CORE
- depends on ARM || COMPILE_TEST
+ depends on ARM
help
This driver is for the on-chip Asychronous Serial Controller on
STMicroelectronics STi SoCs.
diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
index 8b2d735..adadbc1 100644
--- a/drivers/tty/serial/st-asc.c
+++ b/drivers/tty/serial/st-asc.c
@@ -151,12 +151,12 @@ 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)
{
- writel(value, port->membase + offset);
+ writel_relaxed(value, port->membase + offset);
}
/*
--
1.9.3
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 3.17-rc3] serial: asc: Adopt readl_/writel_relaxed()
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
1 sibling, 1 reply; 5+ messages in thread
From: Greg Kroah-Hartman @ 2014-09-08 23:27 UTC (permalink / raw)
To: Daniel Thompson
Cc: linux-kernel, patches, linaro-kernel, Srinivas Kandagatla,
Patrice Chotard, Jiri Slaby, kernel, linux-serial
On Wed, Sep 03, 2014 at 01:00:51PM +0100, Daniel Thompson wrote:
> The architectures where this peripheral exists (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 absense of spin locks during console I/O) if it uses the
> relaxed variants.
>
> This change means the driver is no longer portable and therefore no
> longer suitable for compile testing.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.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
> Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
> Acked-by: Peter Griffin <peter.griffin@linaro.org>
> ---
> drivers/tty/serial/Kconfig | 2 +-
> drivers/tty/serial/st-asc.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 26cec64d..e9b1735 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1527,7 +1527,7 @@ config SERIAL_FSL_LPUART_CONSOLE
> config SERIAL_ST_ASC
> tristate "ST ASC serial port support"
> select SERIAL_CORE
> - depends on ARM || COMPILE_TEST
> + depends on ARM
I really don't like stuff that does this, sorry. I want to test build
as many drivers as I can. COMPILE_TEST does not mean that the driver is
"portable", only that it builds properly on all platforms.
> help
> This driver is for the on-chip Asychronous Serial Controller on
> STMicroelectronics STi SoCs.
> diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
> index 8b2d735..adadbc1 100644
> --- a/drivers/tty/serial/st-asc.c
> +++ b/drivers/tty/serial/st-asc.c
> @@ -151,12 +151,12 @@ 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);
What plaforms do not provide readl_relaxed()?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 3.17-rc3] serial: asc: Adopt readl_/writel_relaxed()
2014-09-08 23:27 ` Greg Kroah-Hartman
@ 2014-09-09 9:38 ` Daniel Thompson
0 siblings, 0 replies; 5+ messages in thread
From: Daniel Thompson @ 2014-09-09 9:38 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: linux-kernel, patches, linaro-kernel, Patrice Chotard,
Jiri Slaby, kernel, linux-serial, Maxime COQUELIN,
Srinivas Kandagatla
On 09/09/14 00:27, Greg Kroah-Hartman wrote:
> On Wed, Sep 03, 2014 at 01:00:51PM +0100, Daniel Thompson wrote:
>> The architectures where this peripheral exists (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 absense of spin locks during console I/O) if it uses the
>> relaxed variants.
>>
>> This change means the driver is no longer portable and therefore no
>> longer suitable for compile testing.
>>
>> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
>> Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.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
>> Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
>> Acked-by: Peter Griffin <peter.griffin@linaro.org>
>> ---
>> drivers/tty/serial/Kconfig | 2 +-
>> drivers/tty/serial/st-asc.c | 4 ++--
>> 2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
>> index 26cec64d..e9b1735 100644
>> --- a/drivers/tty/serial/Kconfig
>> +++ b/drivers/tty/serial/Kconfig
>> @@ -1527,7 +1527,7 @@ config SERIAL_FSL_LPUART_CONSOLE
>> config SERIAL_ST_ASC
>> tristate "ST ASC serial port support"
>> select SERIAL_CORE
>> - depends on ARM || COMPILE_TEST
>> + depends on ARM
>
> I really don't like stuff that does this, sorry. I want to test build
> as many drivers as I can. COMPILE_TEST does not mean that the driver is
> "portable", only that it builds properly on all platforms.
I originally made this change compilable (and portable) but was asked to
change it during review:
http://thread.gmane.org/gmane.linux.ports.arm.kernel/331027/focus=333911
It sounds like I gave in too quickly. I'll re-post the original version
shortly.
>> help
>> This driver is for the on-chip Asychronous Serial Controller on
>> STMicroelectronics STi SoCs.
>> diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
>> index 8b2d735..adadbc1 100644
>> --- a/drivers/tty/serial/st-asc.c
>> +++ b/drivers/tty/serial/st-asc.c
>> @@ -151,12 +151,12 @@ 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);
>
> What plaforms do not provide readl_relaxed()?
I'd never thought to ask that. However I think the answer is "only those
that use asm-generic/io.h" meaning: blackfin, m68k, metag, openrisc,
score and sparc. I'll look into a patch to fix that...
The reason I never thought much about readl_relaxed() is that the
compilability concerns centre around writel_relaxed() instead. This is
much less widely implemented. It appears mostly on architectures where
writel() is both expensive and (sometimes) overkill. It is currently
found only on: alpha, arm, arm64, avr32, hexagon, microblaze, mips and sh.
My original code to conceal the difference between the two looked like
this (and the change is to a single accessor function, not littered
though the code):
--- cut here ---
static inline void asc_out(struct uart_port *port, u32 offset,
u32 value)
{
+#ifdef writel_relaxed
+ writel_relaxed(value, port->membase + offset);
+ barrier();
+#else
writel(value, port->membase + offset);
+#endif
}
--- cut here ---
Note that barrier() is not needed if our only goal is for the driver to
pass the COMPILE_TEST but was included because different architectures
have different rules about inclusion of barrier() within the _relaxed()
macros making explicit barriers useful if this code were consumed by a
copy 'n paste operation...
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel_relaxed()
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 10:03 ` Daniel Thompson
[not found] ` <CALNtEFgd=Lw3AdO2cq_X66_kVdjRyu8sVKN5UX3tzKS5c6d_JA@mail.gmail.com>
1 sibling, 1 reply; 5+ messages in thread
From: Daniel Thompson @ 2014-09-09 10:03 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Daniel Thompson, linux-kernel, patches, linaro-kernel,
Srinivas Kandagatla, Maxime Coquelin, Patrice Chotard,
Jiri Slaby, kernel, linux-serial
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 3.17-rc3 v2] serial: asc: Adopt readl_/writel_relaxed()
[not found] ` <CALNtEFgd=Lw3AdO2cq_X66_kVdjRyu8sVKN5UX3tzKS5c6d_JA@mail.gmail.com>
@ 2014-09-09 11:15 ` Daniel Thompson
0 siblings, 0 replies; 5+ messages in thread
From: Daniel Thompson @ 2014-09-09 11:15 UTC (permalink / raw)
To: Srinivas Kandagatla
Cc: Greg Kroah-Hartman, linux-kernel, patches, linaro-kernel,
Maxime Coquelin, Patrice Chotard, Jiri Slaby, kernel,
linux-serial
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
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
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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
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