Re: Re: [PATCH V2 2/3] riscv: Add ARCH_HAS_PRETCHW support with Zibop

[Andrew Jones]

On Wed, Jan 03, 2024 at 02:19:49PM +0800, Guo Ren wrote:
> On Tue, Jan 2, 2024 at 6:45 PM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
> >
> >
> > s/Zibop/Zicbop/ <<<$SUBJECT
> okay
> 
> >
> > On Sun, Dec 31, 2023 at 03:29:52AM -0500, guoren@xxxxxxxxxx wrote:
> > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > >
> > > Enable Linux prefetchw primitive with Zibop cpufeature, which preloads
> >
> > Also s/Zibop/Zicbop/ here
> okay, thx.
> 
> >
> > > cache line into L1 cache for the next write operation.
> > >
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > > ---
> > >  arch/riscv/include/asm/processor.h | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > >
> > > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > > index f19f861cda54..8d3a2ab37678 100644
> > > --- a/arch/riscv/include/asm/processor.h
> > > +++ b/arch/riscv/include/asm/processor.h
> > > @@ -13,6 +13,9 @@
> > >  #include <vdso/processor.h>
> > >
> > >  #include <asm/ptrace.h>
> > > +#include <asm/insn-def.h>
> > > +#include <asm/alternative-macros.h>
> > > +#include <asm/hwcap.h>
> > >
> > >  #ifdef CONFIG_64BIT
> > >  #define DEFAULT_MAP_WINDOW   (UL(1) << (MMAP_VA_BITS - 1))
> > > @@ -106,6 +109,19 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,
> > >  #define KSTK_EIP(tsk)                (task_pt_regs(tsk)->epc)
> > >  #define KSTK_ESP(tsk)                (task_pt_regs(tsk)->sp)
> > >
> > > +#ifdef CONFIG_RISCV_ISA_ZICBOP
> > > +#define ARCH_HAS_PREFETCHW
> > > +
> > > +#define PREFETCHW_ASM(x)                                             \
> > > +     ALTERNATIVE(__nops(1), CBO_PREFETCH_W(x, 0), 0,                 \
> > > +                 RISCV_ISA_EXT_ZICBOP, CONFIG_RISCV_ISA_ZICBOP)
> > > +
> > > +
> > > +static inline void prefetchw(const void *x)
> > > +{
> > > +     __asm__ __volatile__(PREFETCHW_ASM(%0) : : "r" (x) : "memory");
> > > +}
> >
> > Shouldn't we create an interface which exposes the offset input of
> > the instruction, allowing a sequence of calls to be unrolled? But
> > I guess that could be put off until there's a need for it.
> I want to put it off until there's a user. Let's keep the whole
> imm[11:0] zero for the current.

Yeah, my suggestion didn't make sense in this context anyway since we need
to match the interface in linux/prefetch.h. Considering linux/prefetch.h,
is there some reason we don't also add prefetch() at the same time?

Thanks,
drew

> 
> >
> > > +#endif /* CONFIG_RISCV_ISA_ZICBOP */
> > >
> > >  /* Do necessary setup to start up a newly executed thread. */
> > >  extern void start_thread(struct pt_regs *regs,
> > > --
> > > 2.40.1
> > >
> >
> > Thanks,
> > drew
> 
> 
> 
> -- 
> Best Regards
>  Guo Ren