Re: [PATCH 09/21] riscv: dma-mapping: skip invalidation before bidirectional DMA

Palmer Dabbelt
2023-04-19T14:23:03Z

On Mon, 27 Mar 2023 05:13:05 PDT (-0700), arnd@kernel.org wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> For a DMA_BIDIRECTIONAL transfer, the caches have to be cleaned
> first to let the device see data written by the CPU, and invalidated
> after the transfer to let the CPU see data written by the device.
>
> riscv also invalidates the caches before the transfer, which does
> not appear to serve any purpose.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> arch/riscv/mm/dma-noncoherent.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index 640f4c496d26..69c80b2155a1 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -25,7 +25,7 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> break;
> case DMA_BIDIRECTIONAL:
> - ALT_CMO_OP(flush, vaddr, size, riscv_cbom_block_size);
> + ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> break;
> default:
> break;

Acked-by: Palmer Dabbelt <palmer@rivosinc.com>