Re: [PATCH 2/3] firmware: qcom: scm: Add function to set the maximum IOMMU pool size

[AngeloGioacchino Del Regno]

Il 09/12/21 00:44, Marijn Suijten ha scritto:
> On 2021-12-08 07:30:28, Alex Elder wrote:
> > On 12/8/21 2:34 AM, Marijn Suijten wrote:
> > > From: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxxx>
> > >
> > > This is not necessary for basic functionality of the IOMMU, but
> > > it's an optimization that tells to the TZ what's the maximum
> > > mappable size for the secure IOMMUs, so that it can optimize
> > > the data structures in the TZ itself.
> >
> > Are there no users of this function?	-Alex
>
> I should have probably mentioned in the cover letter that this function
> and the one introduced in patch 3/3 are going to be used in upcoming
> patches for IOMMUs found in msm8976, msm8974 and related SoCs (with the
> side-note that I don't see this particular set_cp_pool_size used in the
> branch that this was submitted from, but it's most likely used elsewhere
> or planned ahead to be used in the near future - I expect Angelo to be
> able to comment on that more accurately).

This function is used in the secured iommu pagetable setup, but not for
all of the "SCM feature versions" (only for version >= 1.1.1, downstream
reads it with a call to scm_feat_version()).

It's not strictly necessary for functionality, hence why Marijn isn't
seeing any call to this in the branch that he was browsing: the spirit here
is to first introduce code that does a minimal (but, of course, working)
setup of the IOMMUs found in MSM8956/76 (which can be adapted with very
minimal changes to other SoCs), and *only then* to add these performance
enhancements to the mix.

...and this is why this commit is here :))

By the way, if my memory isn't failing me, that SCM call should be usable
on all AArch64 SoCs (so, 8956, 8994 and the rest).