Re: [PATCH] xen/arm: smmuv3: remove unused function

[Julien Grall <julien@xxxxxxx>]

Hi Stewart,

On 12/12/2022 16:00, Stewart Hildebrand wrote:
> When building with clang 12 and CONFIG_ARM_SMMU_V3=y, we observe the
> following build error:
>
> drivers/passthrough/arm/smmu-v3.c:1408:20: error: unused function 
> 'arm_smmu_disable_pasid' [-Werror,-Wunused-function]
> static inline void arm_smmu_disable_pasid(struct arm_smmu_master *master) { }
>                     ^
>
> Remove the function.
>
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> ---
> There is also a definition of arm_smmu_disable_pasid() just above,
> guarded by #ifdef CONFIG_PCI_ATS. Should this one be removed too? It
> might be nice to keep this definition for ease of backporting patches
> from Linux, but if we ever plan on supporting PCI_ATS in Xen this may
> need to be re-visited.
Given the function is not called at all, I think this is a bit odd to 
remove the stub but leave the implementation when CONFIG_PCI_ATS is defined.
Rahul, do you plan to use it in the PCI passthrough code? If yes, then I 
would consider to use __maybe_unused.
> This is a candidate for backport to 4.17, 4.16, and possibly 4.15,
> although 4.15 has other issues with clang 12.
The SMMUv3 is a tech preview feature. So we don't usually backport 
fixes. I don't see any reason to diverge here.
Also, note that 4.15 is in any case only security supported since 
October 2022. So such patch would not qualify for backport.
Cheers,

--
Julien Grall