On Sat, Aug 10, 2013 at 11:02:38AM -0300, Ezequiel Garcia wrote: > 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?
Answering myself... How about using drivers/mfd/syscon.c to create the regmap owner for the shared register (TIMER_CTRL in this case, but others might appear) ? Or adding a new mfd implementation if syscon does not fit ? Does this sound like an overkill ? -- 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/