Re: [PATCH net-next 2/4] io: add function to flush the write combine buffer to device immediately

[huangguangbin (A)]

On 2021/7/30 17:00, Will Deacon wrote:
> Hi,
>
> On Fri, Jul 30, 2021 at 11:14:22AM +0800, Guangbin Huang wrote:
> > From: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Signed-off-by: Guangbin Huang <huangguangbin2@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/io.h | 2 ++
> >   include/linux/io.h          | 6 ++++++
> >   2 files changed, 8 insertions(+)
>
> -ENODOCUMENTATION
Hi Will, may I consult you which document file is good to add documentation?

> > 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
> .