[PATCH 2/2] firmware: arm_ffa: Fall back to minimum buffer size if RXTX_MAP fails

[Seth Forshee]

On Tue, Jun 02, 2026 at 05:29:37PM +0100, Sudeep Holla wrote:
> On Tue, Jun 02, 2026 at 11:21:33AM -0500, Seth Forshee wrote:
> > On Tue, Jun 02, 2026 at 04:48:11PM +0100, Sudeep Holla wrote:
> > > On Mon, Jun 01, 2026 at 03:45:12PM -0500, Seth Forshee wrote:
> > > > FFA_FEATURES only supports a maximum size value for RXTX_MAP in v1.2+.
> > > > Older implementations may still reject larger sizes, which can happen
> > > > when the minimum size is rounded up to the page size when PAGE_SIZE >
> > > > 4K.
> > > > 
> > > > Fall back to the minimum size when RXTX_MAP fails with
> > > > INVALID_PARAMETERS to fix the regression on these platforms. This also
> > > > has the side effect of falling back for v1.2+ with a maximum of 0 (i.e.
> > > > no maximum), where the rounded-up value isn't expected to be rejected,
> > > > but there's no harm in retrying with a smaller size and it might even be
> > > > of benefit for a non-compliant SPMC.
> > > > 
> > > 
> > > Is this needed on any of your platforms ? I don't want to push a solution
> > > or fallback/workaround if there are no users for it.
> > 
> > Yes, we have platforms for which commit 83210251fd70 causes RXTX_MAP
> > failures with page sizes larger than 4K.
> >
> 
> And they are FF-A v1.1 or doesn't set max_buf size ? Sorry for being
> pedantic, just want to be sure it is useful on real platforms before
> pushing it as fix/workaround.

Yes, sorry, that's information I should have included. Some were v1.1,
don't set max buf size, and did fail with 64K pages. While I tested the
fix with 16K pages for thoroughness, I did not try to reproduce the
problem with that page size, so I can't say whether or not that would
succeed. But either way there's still a problem, and I figure that going
with the minimum size in that case is the surest bet.

Seth