Re: [PATCH v7 1/6] riscv: mm: dma-noncoherent: Switch using function pointers for cache management

[Conor Dooley]

On Fri, Mar 31, 2023 at 11:37:30AM +0100, Lad, Prabhakar wrote:

> > As far as I recall, the #else path here was needed previously
> > to work around a binutils dependency, but with the current
> > code, it should be possible to just always enable
> > CONFIG_RISCV_ISA_ZICBOM when RISCV_DMA_NONCOHERENT is used.
> >
> Are you suggesting something like below?
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 4dadf35ac721..a55dee98ccf8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -242,6 +242,7 @@ config RISCV_DMA_NONCOHERENT
>         select ARCH_HAS_SYNC_DMA_FOR_CPU
>         select ARCH_HAS_SYNC_DMA_FOR_DEVICE
>         select DMA_DIRECT_REMAP
> +       select RISCV_ISA_ZICBOM
> 
>  config AS_HAS_INSN
>         def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma)
> t0$(comma) t0$(comma) zero)
> @@ -465,7 +466,6 @@ config RISCV_ISA_ZICBOM
>         depends on MMU
>         depends on RISCV_ALTERNATIVE
>         default y
> -       select RISCV_DMA_NONCOHERENT
>         help
>            Adds support to dynamically detect the presence of the ZICBOM
>            extension (Cache Block Management Operations) and enable its
>

Does that actually work? I don't think it does.
If you try to enable RISCV_ISA_ZICBOM then you won't get
RISC_DMA_NONCOHERENT turned on. Run menuconfig and disable support for
Renesas, SiFive and T-Head SoCs & you can replicate.

I think one of RISCV_ISA_ZICBOM and RISCV_DMA_NONCOHERENT should just be
dropped, although I don't know which one to pick!
Making RISCV_DMA_NONCOHERENT user selectable probably makes the most
sense.

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