linux-kernel - Re: ehci-pci breakage with dma-mapping changes in 5.4-rc2

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Date:   Mon, 7 Oct 2019 13:54:32 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Christoph Hellwig <hch@....de>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>, linux-kernel@...r.kernel.org
Subject: Re: ehci-pci breakage with dma-mapping changes in 5.4-rc2

On Mon, Oct 07, 2019 at 09:34:48AM +0200, Christoph Hellwig wrote:
> Hi Arvind,
> 
> can you try the patch below?
> 
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 3f974919d3bd..52b709bf2b55 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -3775,6 +3775,13 @@ static int intel_map_sg(struct device *dev, struct scatterlist *sglist, int nele
>  	return nelems;
>  }
>  
> +static u64 intel_get_required_mask(struct device *dev)
> +{
> +	if (!iommu_need_mapping(dev))
> +		return dma_direct_get_required_mask(dev);
> +	return DMA_BIT_MASK(32);
> +}
> +
>  static const struct dma_map_ops intel_dma_ops = {
>  	.alloc = intel_alloc_coherent,
>  	.free = intel_free_coherent,
> @@ -3787,6 +3794,7 @@ static const struct dma_map_ops intel_dma_ops = {
>  	.dma_supported = dma_direct_supported,
>  	.mmap = dma_common_mmap,
>  	.get_sgtable = dma_common_get_sgtable,
> +	.get_required_mask = intel_get_required_mask,
>  };
>  
>  static void

It doesn't boot with the patch. Won't it go
	dma_get_required_mask
	-> intel_get_required_mask
	-> iommu_need_mapping
	-> dma_get_required_mask
?

Should the call to dma_get_required_mask in iommu_need_mapping be
replaced with dma_direct_get_required_mask on top of your patch?