Message-Id: <20251231114257.2382820-1-vijayanand.jitta@oss.qualcomm.com>
Date: Wed, 31 Dec 2025 17:12:54 +0530
From: Vijayanand Jitta <vijayanand.jitta@....qualcomm.com>
To: robin.murphy@....com, will@...nel.org, joro@...tes.org, robh@...nel.org,
        dmitry.baryshkov@....qualcomm.com, konrad.dybcio@....qualcomm.com,
        bjorn.andersson@....qualcomm.com, bod@...nel.org, conor+dt@...nel.org,
        krzk+dt@...nel.org, saravanak@...gle.com,
        prakash.gupta@....qualcomm.com, vikash.garodia@....qualcomm.com
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Vijayanand Jitta <vijayanand.jitta@....qualcomm.com>
Subject: [PATCH v4 0/3]  of: parsing of multi #{iommu,msi}-cells in maps

So far our parsing of {iommu,msi}-map properites 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[1] 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.
							-- Robin.

Unlike single #{}-cell, it is complex to establish a linear relation
between input 'id' and output specifier for multi-cell properties, thus
it is always expected that len never going to be > 1. 

The motivation for this patchset originates from the multi-map use case
described in V1, which will be addressed in a subsequent series once the
current fixes for iommu-cell handling are concluded.

These changes have been tested on QEMU for the arm64 architecture. We
plan to perform more extensive testing based on community feedback.

[1] https://lore.kernel.org/all/20250627-video_cb-v3-0-51e18c0ffbce@quicinc.com/

V4:
  1) Added Reviewed-by tag.
  2) Resolved warnings reported by kernel test bot, minor code
  reorganization.

  Link to V3:
  https://lore.kernel.org/all/20251221213602.2413124-1-vijayanand.jitta@oss.qualcomm.com/

V3:
  1) Added Reviewed-by tag.
  2) Updated of_map_id_args struct as a wrapper to of_phandle_args and
  added comment description as suggested by Rob Herring.

  Link to V2:
  https://lore.kernel.org/all/20251204095530.8627-1-vijayanand.jitta@oss.qualcomm.com/

V2:
  1) Incorporated the patches from Robin that does the clean implementation.
  2) Dropped the patches the were adding multi-map support from this series
  as suggested.

V1:
 https://lore.kernel.org/all/cover.1762235099.git.charan.kalla@oss.qualcomm.com/

RFC:
 https://lore.kernel.org/all/20250928171718.436440-1-charan.kalla@oss.qualcomm.com/#r

Charan Teja Kalla (1):
  of: factor arguments passed to of_map_id() into a struct

Robin Murphy (2):
  of: Add convenience wrappers for of_map_id()
  of: Respect #{iommu,msi}-cells in maps

 drivers/cdx/cdx_msi.c                    |   3 +-
 drivers/iommu/of_iommu.c                 |  12 +-
 drivers/irqchip/irq-gic-its-msi-parent.c |   4 +-
 drivers/of/base.c                        | 145 +++++++++++++++++------
 drivers/of/irq.c                         |   3 +-
 drivers/pci/controller/dwc/pci-imx6.c    |  10 +-
 drivers/pci/controller/pcie-apple.c      |   6 +-
 drivers/xen/grant-dma-ops.c              |  21 ++--
 include/linux/of.h                       |  36 +++++-
 9 files changed, 169 insertions(+), 71 deletions(-)

-- 
2.34.1

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