Re: [PATCH v8 1/5] dt-bindings: reserved-memory: Document iommu-addresses

[Janne Grunau <j@jannau.net>]

On 2022-09-08 17:32:47 -0500, Rob Herring wrote:
> On Mon, Sep 05, 2022 at 07:08:29PM +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > This adds the "iommu-addresses" property to reserved-memory nodes, which
> > allow describing the interaction of memory regions with IOMMUs. Two use-
> > cases are supported:
> > 
> >   1. Static mappings can be described by pairing the "iommu-addresses"
> >      property with a "reg" property. This is mostly useful for adopting
> >      firmware-allocated buffers via identity mappings. One common use-
> >      case where this is required is if early firmware or bootloaders
> >      have set up a bootsplash framebuffer that a display controller is
> >      actively scanning out from during the operating system boot
> >      process.
> > 
> >   2. If an "iommu-addresses" property exists without a "reg" property,
> >      the reserved-memory node describes an IOVA reservation. Such memory
> >      regions are excluded from the IOVA space available to operating
> >      system drivers and can be used for regions that must not be used to
> >      map arbitrary buffers.
> > 
> > Each mapping or reservation is tied to a specific device via a phandle
> > to the device's device tree node. This allows a reserved-memory region
> > to be reused across multiple devices.
> > 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> > Changes in v8:
> > - include validation warning fixes that had crept into an unrelated patch
> > 
> > Changes in v7:
> > - keep reserved-memory.txt to avoid broken references
> > 
> > Changes in v6:
> > - add device phandle to iommu-addresses property in examples
> > - remove now unused dt-bindings/reserved-memory.h header
> > 
> >  .../reserved-memory/reserved-memory.yaml      | 70 +++++++++++++++++++
> >  1 file changed, 70 insertions(+)
> 
> Thanks for being persistent with this. It looks good to me.
> 
> Reviewed-by: Rob Herring <robh@kernel.org>
> 
> I really don't like new common bindings with only 1 user, so I hope the 
> Asahi folks chime in here. Or really anyone else look at it.

The Asahi WIP display controller/processor driver uses this binding with 
static non 1:1 mappings. The binding is sufficient for our needs our 
needs.

Janne