Re: [PATCH] riscv: add ARCH_DMA_MINALIGN support

[Xianting TIan]

在 2021/8/9 上午12:30, Jisheng Zhang 写道:
> On Sat,  7 Aug 2021 22:55:37 +0800
> Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx> wrote:
>
> > Introduce ARCH_DMA_MINALIGN to riscv arch.
> >
> > Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/riscv/include/asm/cache.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
> > index 9b58b1045..2945bbe2b 100644
> > --- a/arch/riscv/include/asm/cache.h
> > +++ b/arch/riscv/include/asm/cache.h
> > @@ -11,6 +11,8 @@
> >   
> >   #define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)
> >   
> > +#define ARCH_DMA_MINALIGN	L1_CACHE_BYTES
> It's not a good idea to blindly set this for all riscv. For "coherent"
> platforms, this is not necessary and will waste memory.
thanks for the reply,

So riscv is the "coherent" platform?

I submit this patch as I got a fix suggestion of another patch to use 
ARCH_DMA_MINALIGN, but riscv doesn't define it.

https://lkml.org/lkml/2021/8/6/723 <https://lkml.org/lkml/2021/8/6/723>

Considering the portability of the code, in my opinion, it is better to 
define it for riscv if it is not "coherent" platform.

> > +
> >   /*
> >    * RISC-V requires the stack pointer to be 16-byte aligned, so ensure that
> >    * the flat loader aligns it accordingly.