Re: [PATCH 1/6] swiotlb: Add helper to know if it is in use for a specific device.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Aug 26, 2015 at 02:52:02PM -0400, jglisse@redhat.com wrote:
> From: Jérôme Glisse <jglisse@redhat.com>
> 
> Some device like GPU do things differently if swiotlb is in use. We
> use to rely on swiotlb_nr_tbl() to know if swiotlb was enabled or not
> but this is unreliable. Patch add a simple helpers to check if any of

Why is it unreliable?

> the dma_ops associated with a device points to the swiotlb functions,
> making swiotlb check reliable for a device.
> 
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: lkml@vger.kernel.org
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  include/linux/dma-mapping.h | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index ac07ff0..eac911e 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -314,4 +314,22 @@ static inline int dma_mmap_writecombine(struct device *dev,
>  #define dma_unmap_len_set(PTR, LEN_NAME, VAL)    do { } while (0)
>  #endif
>  
> +
> +#ifdef CONFIG_SWIOTLB
> +static inline bool swiotlb_in_use(struct device *dev)
> +{
> +	struct dma_map_ops *ops = get_dma_ops(dev);
> +
> +	return (ops->map_sg == swiotlb_map_sg_attrs ||
> +		ops->unmap_sg == swiotlb_unmap_sg_attrs ||
> +		ops->map_page == swiotlb_map_page);

That won't work. What if we use xen-swiotlb which has different function
names?

> +}
> +#else
> +static inline bool swiotlb_in_use(struct device *dev)
> +{
> +	return false;
> +}
> +#endif
> +
> +
>  #endif
> -- 
> 2.1.0
> 
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