Re: [PATCH 12/12] ARM: mmu: Make sure DMA coherent memory is zeroed out

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Thu, Jan 17, 2019 at 1:36 PM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> Hi Andrey.
>
> On Wed, Jan 16, 2019 at 10:38:40PM -0800, Andrey Smirnov wrote:
> > In order to avoid passing random/junky values to DMA/HW as well as to
> > allow simplifying memory initialization in individual drivers, chagnge
> chagnge => change
>
> > dma_alloc_coherent() to guarantee that memory it returs is properly
> returs => returns
> > zeroed out.

Ugh, will fix the typos.

> >
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> > ---
> >  arch/arm/cpu/mmu-common.c | 3 ++-
> >  arch/arm/cpu/mmu-common.h | 1 +
> >  arch/arm/cpu/mmu.c        | 2 +-
> >  arch/arm/cpu/mmu_64.c     | 8 ++++++++
> >  4 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/cpu/mmu-common.c b/arch/arm/cpu/mmu-common.c
> > index c5b24bff8..aeefbb2da 100644
> > --- a/arch/arm/cpu/mmu-common.c
> > +++ b/arch/arm/cpu/mmu-common.c
> > @@ -43,7 +43,8 @@ void *dma_alloc_map(size_t size, dma_addr_t *dma_handle, unsigned flags)
> >       if (dma_handle)
> >               *dma_handle = (dma_addr_t)ret;
> >
> > -     dma_inv_range(ret, size);
> > +     memset(ret, 0, size);
> > +     dma_flush_range(ret, size);
> >
> >       arch_remap_range(ret, size, flags);
> >
> > diff --git a/arch/arm/cpu/mmu-common.h b/arch/arm/cpu/mmu-common.h
> > index 679799c3c..0a33b138e 100644
> > --- a/arch/arm/cpu/mmu-common.h
> > +++ b/arch/arm/cpu/mmu-common.h
> > @@ -2,6 +2,7 @@
> >  #define __ARM_MMU_COMMON_H
> >
> >  void dma_inv_range(void *ptr, size_t size);
> > +void dma_flush_range(void *ptr, size_t size);
> >  void *dma_alloc_map(size_t size, dma_addr_t *dma_handle, unsigned flags);
> >  void __mmu_init(bool mmu_on);
> >
> > diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
> > index 9e261a0be..29816ad56 100644
> > --- a/arch/arm/cpu/mmu.c
> > +++ b/arch/arm/cpu/mmu.c
> > @@ -97,7 +97,7 @@ static u32 *find_pte(unsigned long adr)
> >       return &table[(adr >> PAGE_SHIFT) & 0xff];
> >  }
> >
> > -static void dma_flush_range(void *ptr, size_t size)
> > +void dma_flush_range(void *ptr, size_t size)
> >  {
> >       unsigned long start = (unsigned long)ptr;
> >       unsigned long end = start + size;
> > diff --git a/arch/arm/cpu/mmu_64.c b/arch/arm/cpu/mmu_64.c
> > index a3074b10d..b45a69661 100644
> > --- a/arch/arm/cpu/mmu_64.c
> > +++ b/arch/arm/cpu/mmu_64.c
> > @@ -233,6 +233,14 @@ void dma_inv_range(void *ptr, size_t size)
> >       v8_inv_dcache_range(start, end);
> >  }
> >
> > +void dma_flush_range(void *ptr, size_t size)
> > +{
> > +     unsigned long start = (unsigned long)ptr;
> > +     unsigned long end = start + size - 1;
> > +
> > +     v8_flush_dcache_range(start, end);
> > +}
> We should use the existing indirection with struct cache_fns
> here, then we could share the code.

AArch64 used to use struct cache_fns, but that approach was decided
against in 4b57aae26c0ada3139ccb1011bdcbd88dc7e1a91 ("ARM: Create own
cache.c file for aarch64") by Sascha. My interpretation of it is that
adding struct cache_fns back would not be particularly welcome, but I
am more that happy to do it if told otherwise.

Thanks,
Andrey Smirnov

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