[PATCH] Revert "powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs"

[Michael Ellerman]

Frederic Barrat <fbarrat at linux.ibm.com> writes:
> On 27/05/2021 04:13, Alexey Kardashevskiy wrote:
>> On 27/05/2021 00:45, Frederic Barrat wrote:
>>> This reverts commit 3c0468d4451eb6b4f6604370639f163f9637a479.
>>>
>>> That commit was breaking alignment guarantees for the DMA address when
>>> allocating coherent mappings, as described in
>>> Documentation/core-api/dma-api-howto.rst
>>>
>>> It was also noticed by Mellanox' driver:
>>> [ 1515.763621] mlx5_core c002:01:00.0: 
>>> mlx5_frag_buf_alloc_node:146:(pid 13402): unexpected map alignment: 
>>> 0x0800000000c61000, page_shift=16
>>> [ 1515.763635] mlx5_core c002:01:00.0: mlx5_cqwq_create:181:(pid
>>> 13402): mlx5_frag_buf_alloc_node() failed, -12
>>>
>>> Signed-off-by: Frederic Barrat <fbarrat at linux.ibm.com>
>> 
>> Should it be
>> 
>> Fixes: 3c0468d4451e ("powerpc/kernel/iommu: Align size for 
>> IOMMU_PAGE_SIZE() to save TCEs")
>> 
>> ?
>
>
> I had been wondering the same... I can see many revert commits with and 
> without a "Fixes:" line. Since here the offending commit was merged in 
> the latest merge window, I was thinking Fixes doesn't really bring 
> anything, it will all stay internal to v5.13 development.

It is still valuable, even if the fix lands in the same release as the
original commit.

The original commit could have been backported elsewhere, so the Fixes
tag is still useful in that case.

> I'd be happy to hear of the expected way of handling it. I'm guessing
> a big part of the answer is whether the tooling looking for a "Fixes"
> line is also looking for reverts.

Tooling should look for both Fixes and reverts, because not everyone is
going to remember to add Fixes tags to a revert.

But I think it's still helpful to include the Fixes tag, I sometimes
grep the commit log for "Fixes: <sha>" and I'm sure others do too.

I've added it to this commit, no need to resend.

cheers