Re: [PATCH 15/15] dma-mapping: bypass indirect calls for dma-direct

Marek Szyprowski
2018-12-14T14:32:43Z

Hi Christoph,

On 2018-12-14 15:24, Christoph Hellwig wrote:
> On Fri, Dec 14, 2018 at 03:11:37PM +0100, Marek Szyprowski wrote:
>> Hi Christoph,
>>
>> On 2018-12-07 20:07, Christoph Hellwig wrote:
>>> Avoid expensive indirect calls in the fast path DMA mapping
>>> operations by directly calling the dma_direct_* ops if we are using
>>> the directly mapped DMA operations.
>>>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> This breaks direct DMA on ARM64 (also todays linux-next). NULL
>> dev->dma_ops fallbacks to get_arch_dma_ops(), which in turn returns
>> non-functional &dma_dummy_ops on ARM64...
> Yeah, fallback from direct (NULL) dev->dma_ops to something else won't
> work with NULL as the indicator.
>
> Fortunately we shouldn't even need that thanks to the patch from Robin
> that explicitly set the dummy ops where needed.
>
> Can you try the patch below?

Yes, it fixes the problem.

> diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
> index 273e778f7de2..95dbf3ef735a 100644
> --- a/arch/arm64/include/asm/dma-mapping.h
> +++ b/arch/arm64/include/asm/dma-mapping.h
> @@ -26,11 +26,7 @@
>
> static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
> {
> - /*
> - * We expect no ISA devices, and all other DMA masters are expected to
> - * have someone call arch_setup_dma_ops at device creation time.
> - */
> - return &dma_dummy_ops;
> + return NULL;
> }
>
> void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>
>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland