Re: [PATCH v2 1/4] dt-bindings: iommu: rockchip: Convert IOMMU to DT schema

[Rob Herring <robh@kernel.org>]

On Thu, Apr 22, 2021 at 02:16:53PM -0300, Ezequiel Garcia wrote:
> (Adding Kever)
> 
> Hi Benjamin,
> 
> Thanks a lot for working on this, it looks amazing. Together with the great work
> that Rockchip is doing, it seems RK3566/RK3568 will have decent support very soon.
> 
> One comment here:
> 
> On Thu, 2021-04-22 at 16:15 +0200, Benjamin Gaignard wrote:
> > Convert Rockchip IOMMU to DT schema
> > 
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> > ---
> > version 2:
> >  - Change maintainer
> >  - Change reg maxItems
> >  - Change interrupt maxItems
> > 
> >  .../bindings/iommu/rockchip,iommu.txt         | 38 ---------
> >  .../bindings/iommu/rockchip,iommu.yaml        | 79 +++++++++++++++++++
> >  2 files changed, 79 insertions(+), 38 deletions(-)
> >  delete mode 100644 Documentation/devicetree/bindings/iommu/rockchip,iommu.txt
> >  create mode 100644 Documentation/devicetree/bindings/iommu/rockchip,iommu.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/iommu/rockchip,iommu.txt b/Documentation/devicetree/bindings/iommu/rockchip,iommu.txt
> > deleted file mode 100644
> > index 6ecefea1c6f9..000000000000
> > --- a/Documentation/devicetree/bindings/iommu/rockchip,iommu.txt
> > +++ /dev/null
> > @@ -1,38 +0,0 @@
> > -Rockchip IOMMU
> > -==============
> > -
> > -A Rockchip DRM iommu translates io virtual addresses to physical addresses for
> > -its master device.  Each slave device is bound to a single master device, and
> > -shares its clocks, power domain and irq.
> > -
> > -Required properties:
> > -- compatible      : Should be "rockchip,iommu"
> > -- reg             : Address space for the configuration registers
> > -- interrupts      : Interrupt specifier for the IOMMU instance
> > -- interrupt-names : Interrupt name for the IOMMU instance
> > -- #iommu-cells    : Should be <0>.  This indicates the iommu is a
> > -                    "single-master" device, and needs no additional information
> > -                    to associate with its master device.  See:
> > -                    Documentation/devicetree/bindings/iommu/iommu.txt
> > -- clocks          : A list of clocks required for the IOMMU to be accessible by
> > -                    the host CPU.
> > -- clock-names     : Should contain the following:
> > -       "iface" - Main peripheral bus clock (PCLK/HCL) (required)
> > -       "aclk"  - AXI bus clock (required)
> > -
> > -Optional properties:
> > -- rockchip,disable-mmu-reset : Don't use the mmu reset operation.
> > -                              Some mmu instances may produce unexpected results
> > -                              when the reset operation is used.
> > -
> > -Example:
> > -
> > -       vopl_mmu: iommu@ff940300 {
> > -               compatible = "rockchip,iommu";
> > -               reg = <0xff940300 0x100>;
> > -               interrupts = <GIC_SPI 16 IRQ_TYPE_LEVEL_HIGH>;
> > -               interrupt-names = "vopl_mmu";
> > -               clocks = <&cru ACLK_VOP1>, <&cru HCLK_VOP1>;
> > -               clock-names = "aclk", "iface";
> > -               #iommu-cells = <0>;
> > -       };
> > diff --git a/Documentation/devicetree/bindings/iommu/rockchip,iommu.yaml b/Documentation/devicetree/bindings/iommu/rockchip,iommu.yaml
> > new file mode 100644
> > index 000000000000..0db208cf724a
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iommu/rockchip,iommu.yaml
> > @@ -0,0 +1,79 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iommu/rockchip,iommu.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Rockchip IOMMU
> > +
> > +maintainers:
> > +  - Heiko Stuebner <heiko@sntech.de>
> > +
> > +description: |+
> > +  A Rockchip DRM iommu translates io virtual addresses to physical addresses for
> > +  its master device. Each slave device is bound to a single master device and
> > +  shares its clocks, power domain and irq.
> > +
> > +  For information on assigning IOMMU controller to its peripheral devices,
> > +  see generic IOMMU bindings.
> > +
> > +properties:
> > +  compatible:
> > +    const: rockchip,iommu
> > +
> > +  reg:
> > +    minItems: 1
> > +    maxItems: 2
> > +
> > +  interrupts:
> > +    minItems: 1
> > +    maxItems: 2
> > +
> > +  interrupt-names:
> > +    minItems: 1
> > +    maxItems: 2
> > +
> 
> AFAICS, the driver supports handling multiple MMUs, and there's one reg and
> interrupt cell for each MMU. IOW, there's no requirement that maxItems is 2.
> 
> Is there any way we can describe that? Or maybe just allow a bigger maximum?

With #iommu-cells == 0, how would one distinguish which IOMMU is 
associated with a device? IOW, is more that 1 really usable?

If you need more just pick a maxItems value that's either the most seen 
or 'should be enough'TM. If the entries are just multiple instances of 
the same thing, please note that here.

Rob