[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/iommu: smmu: Rework how the SMMU version is detected
On Thu, 24 Dec 2020 at 17:39, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote: > > On 24/12/2020 17:10, Julien Grall wrote: > > > > > > On 24/12/2020 17:00, Andrew Cooper wrote: > >> On 24/12/2020 16:49, Julien Grall wrote: > >>> From: Julien Grall <jgrall@xxxxxxxxxx> > >>> > >>> Clang 11 will throw the following error: > >>> > >>> smmu.c:2284:18: error: cast to smaller integer type 'enum > >>> arm_smmu_arch_version' from 'const void *' > >>> [-Werror,-Wvoid-pointer-to-enum-cast] > >>> smmu->version = (enum arm_smmu_arch_version)of_id->data; > >>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> > >>> The error can be prevented by introduce static variable for each SMMU > >>> version and store a pointer for each of them. > >>> > >>> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx> > >> > >> You can also fix this by casting through (uintptr_t) instead of (enum > >> arm_smmu_arch_version), which wouldn't involve an extra indirection. > > > > I thought about using a different cast, but it feels just papering > > over the issue. > > > > But I don't see what's the problem with the extra indirection... It is > > self-contained and only used during the IOMMU initialization. > > Well - its extra .rodata for the sake of satisfying the compiler in a > specific way. You are making the assumption that I wrote this way only to make the compiler happy. :) While the patch was originally written because of the compiler, we will need to introduce some workaround. So the enum is going to be transformed to a structure. I thought about introducing the structure now, but I felt it was more controversial than this approach. > > Irrespective, all of this looks like it ought to be initdata rather than > runtime data, which is probably a bigger deal than worrying about one > extra pointer access. I thought about that. However, not all the users are in __init yet. So this would technically be a layer violation (runtime function should not use init variable). In practice, I think all the users could be in init. I will check and send a patch. Cheers,
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