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@xxxxxxxxxx> >> Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxx> >> Cc: Patrice Chotard <patrice.chotard@xxxxxx> >> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> >> Cc: Jiri Slaby <jslaby@xxxxxxx> >> Cc: kernel@xxxxxxxxxxx >> Cc: linux-serial@xxxxxxxxxxxxxxx >> Acked-by: Maxime Coquelin <maxime.coquelin@xxxxxx> >> Acked-by: Peter Griffin <peter.griffin@xxxxxxxxxx> >> --- >> 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 I originally made this change compilable (and portable) but was asked to change it during review: http://thread.gmane.org/gmane.linux.ports.arm.kernel/331027/focus=333911 It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... -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
