Messages in this thread | | | Date | Fri, 30 Jul 2021 10:00:57 +0100 | From | Will Deacon <> | Subject | Re: [PATCH net-next 2/4] io: add function to flush the write combine buffer to device immediately |
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Hi,
On Fri, Jul 30, 2021 at 11:14:22AM +0800, Guangbin Huang wrote: > From: Xiongfeng Wang <wangxiongfeng2@huawei.com> > > Device registers can be mapped as write-combine type. In this case, data > are not written into the device immediately. They are temporarily stored > in the write combine buffer and written into the device when the buffer > is full. But in some situation, we need to flush the write combine > buffer to device immediately for better performance. So we add a general > function called 'flush_wc_write()'. We use DGH instruction to implement > this function for ARM64. > > Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com> > Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com> > --- > arch/arm64/include/asm/io.h | 2 ++ > include/linux/io.h | 6 ++++++ > 2 files changed, 8 insertions(+)
-ENODOCUMENTATION
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h > index 7fd836bea7eb..5315d023b2dd 100644 > --- a/arch/arm64/include/asm/io.h > +++ b/arch/arm64/include/asm/io.h > @@ -112,6 +112,8 @@ static inline u64 __raw_readq(const volatile void __iomem *addr) > #define __iowmb() dma_wmb() > #define __iomb() dma_mb() > > +#define flush_wc_write() dgh()
I think it would be worthwhile to look at what architectures other than arm64 offer here. For example, is there anything similar to this on riscv, x86 or power? Doing a quick survery of what's out there might help us define a macro that can be used across multiple architectures.
Thanks,
Will
> /* > * Relaxed I/O memory access primitives. These follow the Device memory > * ordering rules but do not guarantee any ordering relative to Normal memory > diff --git a/include/linux/io.h b/include/linux/io.h > index 9595151d800d..469d53444218 100644 > --- a/include/linux/io.h > +++ b/include/linux/io.h > @@ -166,4 +166,10 @@ static inline void arch_io_free_memtype_wc(resource_size_t base, > } > #endif > > +/* IO barriers */ > + > +#ifndef flush_wc_write > +#define flush_wc_write() do { } while (0) > +#endif > + > #endif /* _LINUX_IO_H */ > -- > 2.8.1 >
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