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[v11,0/5] iommu: Support mappings/reservations in reserved-memory regions

Message ID 20221111161806.630527-1-thierry.reding@gmail.com
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Series iommu: Support mappings/reservations in reserved-memory regions | expand

Message

Thierry Reding Nov. 11, 2022, 4:18 p.m. UTC 
From: Thierry Reding <treding@nvidia.com>

Hi,

This version has several fixes over the previous v10, which can be found
here:

  https://lore.kernel.org/all/20221103133900.1473855-1-thierry.reding@gmail.com/

Most notably this introduces a better mechanism to deal with DMA address
translation issues caused by a mismatch of #address-cells in child and
DMA parent nodes. This now introduces #dma-address-cells and #dma-size-
cells, which can be used to override #address-cells and #size-cells and
define a DMA bus that can be wider than the control bus.

An example is included in the DT bindings, but here is an extract of
what I've used to test this:

        reserved-memory {
                #address-cells = <2>;
                #size-cells = <2>;
                ranges;

                /*
                 * Creates an identity mapping for the framebuffer that
                 * the firmware has setup to scan out a bootsplash from.
                 */
                fb: framebuffer@92cb2000 {
                        reg = <0x0 0x92cb2000 0x0 0x00800000>;
                        iommu-addresses = <&dc0 0x0 0x92cb2000 0x0 0x00800000>;
                };

                /*
                 * Creates a reservation in the IOVA space to prevent
                 * any buffers from being mapped to that region. Note
                 * that on Tegra the range is actually quite different
                 * from this, but it would conflict with the display
                 * driver that I tested this against, so this is just
                 * a dummy region for testing.
                 */
                adsp: reservation-adsp {
                        iommu-addresses = <&dc0 0x0 0x90000000 0x0 0x00010000>;
                };
        };

        host1x@50000000 {
                dc@54200000 {
                        memory-region = <&fb>, <&adsp>;
                };
        };

This is abbreviated a little to focus on the essentials. Note also that
the ADSP reservation is not actually used on this device and the driver
for this doesn't exist yet, but I wanted to include this variant for
testing, because we'll want to use these bindings for the reservation
use-case as well at some point.

I've also been able to make use of this binding and the IOMMU code in
conjunction with the simple-framebuffer driver to hand over a display
configuration set up by UEFI to the Linux kernel.

Janne has confirmed[0] this to be suitable for indirect mappings as
well, though these patches don't implement that feature yet. Potential
extensions to this have been discussed but are not yet included at this
time to not further complicate things.

Thierry

[0]: https://lore.kernel.org/all/20220909144504.GA4024@jannau.net/



Thierry Reding (5):
  of: Introduce support for #dma-{address,size}-cells
  of: Introduce of_translate_dma_region()
  dt-bindings: reserved-memory: Document iommu-addresses
  iommu: Implement of_iommu_get_resv_regions()
  iommu: dma: Use of_iommu_get_resv_regions()

 .../reserved-memory/reserved-memory.yaml      | 73 ++++++++++++++
 drivers/iommu/dma-iommu.c                     |  3 +
 drivers/iommu/of_iommu.c                      | 94 +++++++++++++++++++
 drivers/of/address.c                          | 84 +++++++++++++----
 drivers/of/base.c                             | 70 +++++++++++---
 drivers/of/of_private.h                       | 14 ++-
 include/linux/of.h                            | 17 +++-
 include/linux/of_address.h                    |  4 +-
 include/linux/of_iommu.h                      |  8 ++
 9 files changed, 329 insertions(+), 38 deletions(-)