Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

Arnd Bergmann
2016-04-27T14:12:07Z

On Wednesday 27 April 2016 14:59:00 Catalin Marinas wrote:
>
> I would be in favour of a dma_inherit() function as well. We could hack
> something up in the arch code (like below) but I would rather prefer an
> explicit dma_inherit() call by drivers creating such devices.
>
> diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
> index ba437f090a74..ea6fb9b0e8fa 100644
> --- a/arch/arm64/include/asm/dma-mapping.h
> +++ b/arch/arm64/include/asm/dma-mapping.h
> @@ -29,8 +29,11 @@ extern struct dma_map_ops dummy_dma_ops;
>
> static inline struct dma_map_ops *__generic_dma_ops(struct device *dev)
> {
> - if (dev && dev->archdata.dma_ops)
> - return dev->archdata.dma_ops;
> + while (dev) {
> + if (dev->archdata.dma_ops)
> + return dev->archdata.dma_ops;
> + dev = dev->parent;
> + }

I think this would be a very bad idea: we don't want to have random
devices be able to perform DMA just because their parent devices
have been set up that way.

Arnd