> 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);
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