On Sat, Aug 10, 2013 at 04:49:28PM +0400, Alexander Shiyan wrote: > > Some SoC have MMIO regions that are shared across orthogonal > > subsystems. This commit implements a possible solution for the > > thread-safe access of such regions through a spinlock-protected API > > with clear-set semantics. > > > > Concurrent access is protected with a single spinlock for the > > entire MMIO address space. While this protects shared-registers, > > it also serializes access to unrelated/unshared registers. > > > > Signed-off-by: Ezequiel Garcia <ezequiel.gar...@free-electrons.com> > > --- > > arch/arm/include/asm/io.h | 5 +++++ > > arch/arm/kernel/io.c | 24 ++++++++++++++++++++++++ > > 2 files changed, 29 insertions(+) > > > > diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h > > index d070741..c84658d 100644 > > --- a/arch/arm/include/asm/io.h > > +++ b/arch/arm/include/asm/io.h > > @@ -36,6 +36,11 @@ > > #define isa_bus_to_virt phys_to_virt > > > > /* > > + * Atomic MMIO-wide IO clear/set > > + */ > > +extern void atomic_io_clear_set(void __iomem *reg, u32 clear, u32 set); > > + > > +/* > > * Generic IO read/write. These perform native-endian accesses. Note > > * that some architectures will want to re-define __raw_{read,write}w. > > */ > > diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c > > index dcd5b4d..3ab8201 100644 > > --- a/arch/arm/kernel/io.c > > +++ b/arch/arm/kernel/io.c > > @@ -1,6 +1,30 @@ > > #include <linux/export.h> > > #include <linux/types.h> > > #include <linux/io.h> > > +#include <linux/spinlock.h> > > + > > +static DEFINE_SPINLOCK(__io_lock); > > + > > +/* > > + * Some platforms have MMIO regions that are shared across orthogonal > > + * subsystems. This API implements thread-safe access to such regions > > + * through a spinlock-protected API with clear-set semantics. > > + * > > + * Concurrent access is protected with a single spinlock for the entire > > MMIO > > + * address space. While this protects shared-registers, it also serializes > > + * access to unrelated/unshared registers. > > + * > > + * Using this API on frequently accessed registers in performance-critical > > + * paths is not recommended, as the spinlock used by this API would become > > + * highly contended. > > + */ > > +void atomic_io_clear_set(void __iomem *reg, u32 clear, u32 set) > > +{ > > + spin_lock(&__io_lock); > > + writel((readl(reg) & ~clear) | set, reg); > > + spin_unlock(&__io_lock); > > +} > > +EXPORT_SYMBOL(atomic_io_clear_set); > > So, one lock is used to all possible registers? > Seems a regmap-mmio can be used for such access. >
Thanks for the hint! Quite frankly, I wasn't familiar with regmap-mmio. However, after reading some code, I fail to see how that helps in this case. Note that we need to access the *same* MMIO address from completely different (and unrelated) drivers, such as watchdog and clocksource. So I wonder who would "own" the regmap descriptor, and how does the other one gets aware of that descriptor? In addition given we can use orion_wdt (originally meant for mach-kirkwood) to support mvebu SoC watchdog, we need to sort this out in a completely multiplatform capable way. Ideas? -- Ezequiel GarcĂa, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/