Re: [PATCH v16 3/3] of: Respect #{iommu,msi}-cells in maps

On Thu, Jul 23, 2026 at 03:17:24PM +0200, Neil Armstrong wrote:
> Hi,
> 
> On 6/3/26 09:13, Vijayanand Jitta wrote:
> > From: Robin Murphy <[email protected]>
> > 
> > So far our parsing of {iommu,msi}-map properties has always blindly
> > assumed that the output specifiers will always have exactly 1 cell.
> > This typically does happen to be the case, but is not actually enforced
> > (and the PCI msi-map binding even explicitly states support for 0 or 1
> > cells) - as a result we've now ended up with dodgy DTs out in the field
> > which depend on this behaviour to map a 1-cell specifier for a 2-cell
> > provider, despite that being bogus per the bindings themselves.
> > 
> > Since there is some potential use in being able to map at least single
> > input IDs to multi-cell output specifiers (and properly support 0-cell
> > outputs as well), add support for properly parsing and using the target
> > nodes' #cells values, albeit with the unfortunate complication of still
> > having to work around expectations of the old behaviour too.
> > 
> > Since there are multi-cell output specifiers, the callers of of_map_id()
> > may need to get the exact cell output value for further processing.
> > Update of_map_id() to set args_count in the output to reflect the actual
> > number of output specifier cells.
> > 
> > Signed-off-by: Robin Murphy <[email protected]>
> > Signed-off-by: Charan Teja Kalla <[email protected]>
> > Signed-off-by: Vijayanand Jitta <[email protected]>
> > ---
> >   drivers/of/base.c  | 168 +++++++++++++++++++++++++++++++++++++++++------------
> >   include/linux/of.h |   6 +-
> >   2 files changed, 135 insertions(+), 39 deletions(-)
> > 
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index d658c2620135..ac7961cbab94 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -2116,19 +2116,49 @@ int of_find_last_cache_level(unsigned int cpu)
> >   	return cache_level;
> >   }
> > +/*
> > + * Some DTs have an iommu-map targeting a 2-cell IOMMU node while
> > + * specifying only 1 cell. Fortunately they all consist of value '1'
> > + * as the 2nd cell entry with the same target, so check for that pattern.
> > + *
> > + * Example:
> > + *	IOMMU node:
> > + *		#iommu-cells = <2>;
> > + *
> > + *	Device node:
> > + *		iommu-map = <0x0000 &smmu 0x0000 0x1>,
> > + *			    <0x0100 &smmu 0x0100 0x1>;
> 
> So the sm8650 PCIe controllers has:
> 
> pcie@1c08000:
> 			iommu-map = <0     &apps_smmu 0x1480 0x1>,
> 				    <0x100 &apps_smmu 0x1481 0x1>;

To silence the warning, update the iommu maps to:

			iommu-map = <0     &apps_smmu 0x1480 0x0 0x1>,
				    <0x100 &apps_smmu 0x1481 0x0 0x1>;


-- 
With best wishes
Dmitry