[U-Boot] [PATCH 2/6] riscv: remove invalid dcache flush implementation

[Rick Chen]

Hi Lukas

Auer, Lukas <lukas.auer at aisec.fraunhofer.de> 於 2019年1月2日 週三 下午8:22寫道：
>
> Hi Rick,
>
> On Wed, 2019-01-02 at 10:54 +0800, Rick Chen wrote:
> > Hi Lukas
> >
> > > > From: Lukas Auer [mailto:lukas.auer at aisec.fraunhofer.de]
> > > > Sent: Monday, December 31, 2018 2:28 AM
> > > > To: u-boot at lists.denx.de
> > > > Cc: Anup Patel; Lukas Auer; Rick Jian-Zhi Chen(陳建志); Bin Meng;
> > > > Greentime Hu
> > > > Subject: [PATCH 2/6] riscv: remove invalid dcache flush
> > > > implementation
> > > >
> > > > The fence instruction is used to enforce device I/O and memory
> > > > ordering
> > > > constraints in RISC-V. It does not directly affect the data cache
> > > > and particular
> > > > cannot be used to flush or invalidate it. RISC-V does not have
> > > > instructions for
> > > > explicit cache control. Remove the flush_dcache_all
> > > > implementation and its use
> > > > in all dcache-specific functions in lib/cache.c.
> > > >
> >
> > The privileged mention that fence is for the purposes of ordering,
> > but
> > does not say
> > it can not be used to flush or invalidate.
> >
> > Andes's ax25 have no coherence agent. So it need fence instruction to
> > manipulate
> > cache flush or invalidate. Or there will be some data synchronization
> > error
> > occurs on ae350 platform.
> >
>
> I was not aware of this. Does the ax25 flush the whole dcache on any
> fence instruction?

Yes.
It will flush the whole dcache when execute fence.

>
> You are right, we can't remove it in this case. Since it is specific to
> the ax25, should I move it into cpu/ax25/cache.c instead?

OK
It is good to me.
And thanks for your understanding and improvements.

Regards
Rick

>
> Thanks,
> Lukas
>
> > Thanks
> > Rick
> >
> >
> > > > This also adds a missing new line between flush_dcache_all and
> > > > flush_dcache_range in lib/cache.c.
> > > >
> > > > Signed-off-by: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
> > > > ---
> > > > This patch only removes the implementation itself and its use in
> > > > dcache-specific
> > > > functions in lib/cache.c. There are more uses of it in
> > > > arch/riscv/, which this patch
> > > > does not remove.
> > > >
> > > >  arch/riscv/lib/cache.c | 4 +---
> > > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > > >
> > > > diff --git a/arch/riscv/lib/cache.c b/arch/riscv/lib/cache.c
> > > > index
> > > > ae5c60716f..203e287612 100644
> > > > --- a/arch/riscv/lib/cache.c
> > > > +++ b/arch/riscv/lib/cache.c
> > > > @@ -13,11 +13,10 @@ void invalidate_icache_all(void)
> > > >
> > > >  void flush_dcache_all(void)
> > > >  {
> > > > -     asm volatile ("fence" :::"memory");
> > > >  }
> > > > +
> > > >  void flush_dcache_range(unsigned long start, unsigned long
> > > > end)  {
> > > > -     flush_dcache_all();
> > > >  }
> > > >
> > > >  void invalidate_icache_range(unsigned long start, unsigned long
> > > > end) @@ -31,7
> > > > +30,6 @@ void invalidate_icache_range(unsigned long start,
> > > > unsigned long end)
> > > >
> > > >  void invalidate_dcache_range(unsigned long start, unsigned long
> > > > end)  {
> > > > -     flush_dcache_all();
> > > >  }
> > > >
> > > >  void cache_flush(void)
> > > > --
> > > > 2.20.1