Subject: Re: [PATCH v6 08/15] swiotlb: Bounce data from/to restricted DMA pool if available

From: Christoph Hellwig <[email-masked]>
Date: Mon, 10 May 2021 17:05:16 +0200

> +static inline bool is_dev_swiotlb_force(struct device *dev)
> +{
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +	if (dev->dma_io_tlb_mem)
> +		return true;
> +#endif /* CONFIG_DMA_RESTRICTED_POOL */
> +	return false;
> +}
> +

>  	/* If SWIOTLB is active, use its maximum mapping size */
>  	if (is_swiotlb_active(dev) &&
> -	    (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
> +	    (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE ||
> +	     is_dev_swiotlb_force(dev)))

This is a mess.  I think the right way is to have an always_bounce flag
in the io_tlb_mem structure instead.  Then the global swiotlb_force can
go away and be replace with this and the fact that having no
io_tlb_mem structure at all means forced no buffering (after a little
refactoring).