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 > <[email protected] <mailto:[email protected]>> 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 <[email protected] > <mailto:[email protected]>> > Cc: Srinivas Kandagatla <[email protected] > <mailto:[email protected]>> > Cc: Maxime Coquelin <[email protected] > <mailto:[email protected]>> > Cc: Patrice Chotard <[email protected] > <mailto:[email protected]>> > Cc: Greg Kroah-Hartman <[email protected] > <mailto:[email protected]>> > Cc: Jiri Slaby <[email protected] <mailto:[email protected]>> > Cc: [email protected] <mailto:[email protected]> > Cc: [email protected] <mailto:[email protected]> > --- > > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
