# Re: \[PATCH RFC v1 2/6\] swiotlb: convert variables to arrays

- From: Robin Murphy \<robin.murphy@arm.com\>
- Date: 2021-02-04 11:50:22 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/02/6258456
- Thread: https://ratatoskr.run/dri-devel/2021/02/6258456/t.md

```text
On 2021-02-04 07:29, Christoph Hellwig wrote:
> On Wed, Feb 03, 2021 at 03:37:05PM -0800, Dongli Zhang wrote:
>> This patch converts several swiotlb related variables to arrays, in
>> order to maintain stat/status for different swiotlb buffers. Here are
>> variables involved:
>>
>> - io_tlb_start and io_tlb_end
>> - io_tlb_nslabs and io_tlb_used
>> - io_tlb_list
>> - io_tlb_index
>> - max_segment
>> - io_tlb_orig_addr
>> - no_iotlb_memory
>>
>> There is no functional change and this is to prepare to enable 64-bit
>> swiotlb.
>
> Claire Chang (on Cc) already posted a patch like this a month ago,
> which looks much better because it actually uses a struct instead
> of all the random variables.

Indeed, I skimmed the cover letter and immediately thought that this whole thing is just the restricted DMA pool concept[1] again, only from a slightly different angle.

Robin.

[1] https://lore.kernel.org/linux-iommu/20210106034124.30560-1-tientzu@chromium.org/
```