Re: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

[Ira Weiny]

On Mon, Feb 24, 2020 at 11:44:44AM -0800, Christoph Hellwig wrote:
> This allows the arch code to reset the page tables to cached access when
> freeing a dma coherent allocation that was set to uncached using
> arch_dma_set_uncached.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  arch/Kconfig                    | 7 +++++++
>  include/linux/dma-noncoherent.h | 1 +
>  kernel/dma/direct.c             | 2 ++
>  3 files changed, 10 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 090cfe0c82a7..c26302f90c96 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -255,6 +255,13 @@ config ARCH_HAS_SET_DIRECT_MAP
>  config ARCH_HAS_DMA_SET_UNCACHED
>  	bool
>  
> +#
> +# Select if the architectures provides the arch_dma_clear_uncached symbol
> +# to undo an in-place page table remap for uncached access.
> +#
> +config ARCH_HAS_DMA_CLEAR_UNCACHED
> +	bool
> +
>  # Select if arch init_task must go in the __init_task_data section
>  config ARCH_TASK_STRUCT_ON_STACK
>  	bool
> diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
> index 1a4039506673..b59f1b6be3e9 100644
> --- a/include/linux/dma-noncoherent.h
> +++ b/include/linux/dma-noncoherent.h
> @@ -109,5 +109,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
>  #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
>  
>  void *arch_dma_set_uncached(void *addr, size_t size);
> +void arch_dma_clear_uncached(void *addr, size_t size);
>  
>  #endif /* _LINUX_DMA_NONCOHERENT_H */
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index f01a8191fd59..a8560052a915 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -219,6 +219,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>  
>  	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
>  		vunmap(cpu_addr);
> +	else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> +		arch_dma_clear_uncached(cpu_addr, size);

Isn't using arch_dma_clear_uncached() before patch 5 going to break
bisectability?

Ira

>  
>  	dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
>  }
> -- 
> 2.24.1
>