Re: [PATCH 18/19] iommu: Update various drivers to pass in lg2sz instead of order to iommu pages

On Wed, Feb 05, 2025 at 06:03:54PM +0000, Robin Murphy wrote:

But what's the benefit of having extra stuff capable of turning a constant
into a different constant that doesn't represent anything we
actually want?

The API is inherently log2 based, like alloc_pages() is. You could
make the same argument that alloc_pages() should accept a size and do
order internally too.

We still end up doing more runtime arithmetic on lg2sz within the allocation
function itself to turn it into the order we ultimately still need, so that
arithmetic could just as well be get_order(size) and have nothing to inline

Okay, sure it isn't fast path or anything. It just seems weird to
start out with a lg2 constant value in most callers, shift it to a
size, then ilog2 it back to a lg2. There are few places that don't
have a compile time lg2 available.

Jason