Messages in this thread | | | Date | Wed, 28 Aug 2013 06:49:08 -0300 | From | Ezequiel Garcia <> | Subject | Re: [PATCH v4 2/4] ARM: Add atomic_io_modify optimized routines |
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On Wed, Aug 28, 2013 at 09:53:40AM +0100, Catalin Marinas wrote: > On Sat, Aug 24, 2013 at 04:35:30PM +0100, Ezequiel Garcia wrote: > > Implement arch-specific atomic_io_modify and atomic_io_modify_relaxed, > > which are based on writel/readl_relaxed and writel_relaxed/readl_relaxed, > > respectively. > > In both cases, by relaxing the readl, perfomance can be improved. > > > > Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com> > > --- > > arch/arm/include/asm/io.h | 4 ++++ > > arch/arm/kernel/io.c | 29 +++++++++++++++++++++++++++++ > > 2 files changed, 33 insertions(+) > > > > diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h > > index d070741..53637b6 100644 > > --- a/arch/arm/include/asm/io.h > > +++ b/arch/arm/include/asm/io.h > > @@ -397,5 +397,9 @@ extern int devmem_is_allowed(unsigned long pfn); > > extern void register_isa_ports(unsigned int mmio, unsigned int io, > > unsigned int io_shift); > > > > +#define __HAVE_ARCH_ATOMIC_IO_MODIFY > > +extern void atomic_io_modify(void __iomem *reg, u32 mask, u32 set); > > +extern void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set); > > + > > #endif /* __KERNEL__ */ > > #endif /* __ASM_ARM_IO_H */ > > diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c > > index dcd5b4d..a8c9c9b 100644 > > --- a/arch/arm/kernel/io.c > > +++ b/arch/arm/kernel/io.c > > @@ -1,6 +1,35 @@ > > #include <linux/export.h> > > #include <linux/types.h> > > #include <linux/io.h> > > +#include <linux/spinlock.h> > > + > > +static DEFINE_RAW_SPINLOCK(__io_lock); > > + > > +void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set) > > +{ > > + unsigned long flags; > > + u32 value; > > + > > + raw_spin_lock_irqsave(&__io_lock, flags); > > + value = readl_relaxed(reg) & ~mask; > > + value |= (set & mask); > > + writel_relaxed(value, reg); > > + raw_spin_unlock_irqrestore(&__io_lock, flags); > > +} > > +EXPORT_SYMBOL(atomic_io_modify_relaxed); > > + > > +void atomic_io_modify(void __iomem *reg, u32 mask, u32 set) > > +{ > > + unsigned long flags; > > + u32 value; > > + > > + raw_spin_lock_irqsave(&__io_lock, flags); > > + value = readl_relaxed(reg) & ~mask; > > + value |= (set & mask); > > + writel(value, reg); > > + raw_spin_unlock_irqrestore(&__io_lock, flags); > > +} > > +EXPORT_SYMBOL(atomic_io_modify); > > Is this any different from the generic one introduced in patch 1/4? I > would rather just use the generic definition.
Well, according to Will Deacon (and as documented in the commit log) we can optimize in ARM by using readl_relaxed instead of readl.
Now, I'm sure you now better than me if that results (or not) in any significant optimization.
> Similarly, a generic > atomic_io_modify_relaxed() but guarded with something like > __HAVE_ARCH_RELAXED_IO. >
No, that's not possible. As far as I understand, there's no guarantee of _relaxed variants to be available architecture-wide. -- Ezequiel García, 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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