# Re: \[PATCH kernel\] powerpc/iommu: Report the correct most efficient DMA mask for PCI devices

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2021-09-30 05:44:06 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/09/9524555
- Thread: https://ratatoskr.run/linuxppc-dev/2021/09/9524554/t.md

```text
On Thu, Sep 30, 2021 at 01:44:54PM +1000, Alexey Kardashevskiy wrote:
> and returns the IOMMU table mask on the pseries platform which makes some
> drivers (mpt3sas is one example) choose 32bit DMA even though bypass is
> supported. The powernv platform sort of handles it by having a bigger
> default window with a mask >=40 but it only works as drivers choose
> 63/64bit if the required mask is >32 which is rather pointless.
> 
> This reintroduces the bypass capability check to let drivers make
> a better choice of the DMA mask.
> 
> Fixes: f1565c24b596 ("powerpc: use the generic dma_ops_bypass mode")
> Signed-off-by: Alexey Kardashevskiy <redacted>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
```