Re: [PATCH 4/4] csky: Add dma_inv_range for DMA_FROM_DEVICE

[Arnd Bergmann <arnd@arndb.de>]

On Tue, Jul 30, 2019 at 2:16 PM <guoren@kernel.org> wrote:
> From: Guo Ren <ren_guo@c-sky.com>

> diff --git a/arch/csky/mm/dma-mapping.c b/arch/csky/mm/dma-mapping.c
> index 3f1ff9d..d8f0f81 100644
> --- a/arch/csky/mm/dma-mapping.c
> +++ b/arch/csky/mm/dma-mapping.c
> @@ -72,6 +72,8 @@ void arch_sync_dma_for_device(struct device *dev, phys_addr_t paddr,
>                 cache_op(paddr, size, dma_wb_range);
>                 break;
>         case DMA_FROM_DEVICE:
> +               cache_op(paddr, size, dma_inv_range);
> +               break;
>         case DMA_BIDIRECTIONAL:
>                 cache_op(paddr, size, dma_wbinv_range);
>                 break;
> @@ -88,6 +90,8 @@ void arch_sync_dma_for_cpu(struct device *dev, phys_addr_t paddr,
>                 cache_op(paddr, size, dma_wb_range);
>                 break;
>         case DMA_FROM_DEVICE:
> +               cache_op(paddr, size, dma_inv_range);
> +               break;
>         case DMA_BIDIRECTIONAL:
>                 cache_op(paddr, size, dma_wbinv_range);
>                 break;

When syncing 'for_cpu', you should not need to write back, because
there won't be any dirty cache lines.

If you have a CPU core that does not do speculative loads, you also don't
need to invalidate here, because you have already done that in the
_for_device() case, the only reason to invalidate the CPU cache
again is if a speculative load created a stale cache line that now
shadows the data received from the device.

        Arnd