On Wed, Jan 18, 2023 at 4:05 PM Simon Glass <sjg@xxxxxxxxxxxx> wrote:
>
> Hi Rob,
>
> On Wed, 18 Jan 2023 at 13:34, Rob Herring <robh@xxxxxxxxxx> wrote:
> >
> > On Fri, Jan 13, 2023 at 2:58 PM Simon Glass <sjg@xxxxxxxxxxxx> wrote:
> > >
> > > U-Boot has some particular challenges with device tree and devices:
> > >
> > > - U-Boot has multiple build phases, such as a Secondary Program Loader
> > > (SPL) phase which typically runs in a pre-SDRAM environment where code
> > > and data space are limited. In particular, there may not be enough
> > > space for the full device tree blob. U-Boot uses various automated
> > > techniques to reduce the size from perhaps 40KB to 3KB. It is not
> > > always possible to handle these tags entirely at build time, since
> > > U-Boot proper must have the full device tree, even though we do not
> > > want it to process all nodes until after relocation.
> > > - Some U-Boot phases needs to run before the clocks are properly set up,
> > > where the CPU may be running very slowly. Therefore it is important to
> > > bind only those devices which are actually needed in that phase
> > > - U-Boot uses lazy initialisation for its devices, with 'bind' and
> > > 'probe' being separate steps. Even if a device is bound, it is not
> > > actually probed until it is used. This is necessary to keep the boot
> > > time reasonable, e.g. to under a second
> > >
> > > The phases of U-Boot in order are: TPL, VPL, SPL, U-Boot (first
> > > pre-relocation, then post-relocation). ALl but the last two are optional.
> > >
> > > For the above reasons, U-Boot only includes the full device tree in the
> > > final 'U-Boot proper' build. Even then, before relocation U-Boot only
> > > processes nodes which are marked as being needed.
> > >
> > > For this to work, U-Boot's driver model[1] provides a way to mark device
> > > tree nodes as applicable for a particular phase. This works by adding a
> > > tag to the node, e.g.:
> > >
> > > cru: clock-controller@ff760000 {
> > > bootph-all;
> > > compatible = "rockchip,rk3399-cru";
> > > reg = <0x0 0xff760000 0x0 0x1000>;
> > > rockchip,grf = <&grf>;
> > > #clock-cells = <1>;
> > > #reset-cells = <1>;
> > > ...
> > > };
> > >
> > > Here the "bootph-all" tag indicates that the node must be present in all
> > > phases, since the clock driver is required.
> > >
> > > There has been discussion over the years about whether this could be done
> > > in a property instead, e.g.
> > >
> > > options {
> > > bootph-all = <&cru> <&gpio_a> ...;
> > > ...
> > > };
> > >
> > > Some problems with this:
> > >
> > > - we need to be able to merge several such tags from different .dtsi files
> > > since many boards have their own specific requirements
> > > - it is hard to find and cross-reference the affected nodes
> > > - it is more error-prone
> > > - it requires significant tool rework in U-Boot, including fdtgrep and
> > > the build system
> > > - is harder (slower, more code) to process since it involves scanning
> > > another node/property to find out what to do with a particular node
> > > - we don't want to add phandle arguments to the above since we are
> > > referring, e.g., to the clock device as a whole, not a paricular clock
> > > - the of-platdata feature[2], which converts device tree to C for even
> > > more constrained environments, would need to become aware of the
> > > /options node
> > >
> > > There is also the question about whether this needs to be U-Boot-specific,
> > > or whether the tags could be generic. From what I can tell, U-Boot is the
> > > only bootloader which seriously attempts to use a runtime device tree in
> > > all cases. For this version, an attempt is made to name the phases in a
> > > generic manner.
> > >
> > > It should also be noted that the approach provided here has stood the test
> > > of time, used in U-Boot for 8 years so far.
> > >
> > > So add the schema for this. This will allow a major class of schema
> > > exceptions to be dropped from the U-Boot source tree.
> > >
> > > This being sent to the mailing list since it might attract more review.
> > > A PR will be sent when this has had some review. That is why the file
> > > path is set up for https://github.com/devicetree-org/dt-schema rather
> > > than the Linux kernel.
> > >
> > > [1] https://u-boot.readthedocs.io/en/latest/develop/driver-model/index.html
> > > [2] https://u-boot.readthedocs.io/en/latest/develop/driver-model/of-plat.html
> > >
> > > Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> > > ---
> > >
> > > Changes in v6:
> > > - Use 'bootph' instead of 'phase'
> > > - Use | instead of , in patternProperties
> > > - Drop mention of 40KB for device-tree size
> > > - Rework description of handling of parent nodes
> > > - Use separate properties for each boot phase
> > > - Update validation example at the top of bootphases.dts
> > >
> > > Changes in v5:
> > > - Fix instructions to run test
> > > - Update binding title
> > > - Use 'phase-' instead of 'phase,'
> > >
> > > Changes in v4:
> > > - Drop some unnecessary context from the commit message
> > > - Explain why parent nodes do not automatically inherit their children's
> > > tags
> > > - Rename the tags to use a phase,xxx format, explaining each one
> > >
> > > Changes in v3:
> > > - Fix an incorrect schema path in $id
> > >
> > > Changes in v2:
> > > - Expand docs to include a description of each tag
> > > - Fix some typos and unclear wording
> > >
> > > dtschema/lib.py | 5 +++
> > > dtschema/schemas/bootph.yaml | 86 ++++++++++++++++++++++++++++++++++++
> > > test/bootphases.dts | 22 +++++++++
> > > 3 files changed, 113 insertions(+)
> > > create mode 100644 dtschema/schemas/bootph.yaml
> > > create mode 100644 test/bootphases.dts
> > >
> > > diff --git a/dtschema/lib.py b/dtschema/lib.py
> > > index c7b6cb9..95a4f10 100644
> > > --- a/dtschema/lib.py
> > > +++ b/dtschema/lib.py
> > > @@ -493,6 +493,11 @@ def fixup_node_props(schema):
> > > schema['properties'].setdefault('status', True)
> > > schema['properties'].setdefault('secure-status', True)
> > > schema['properties'].setdefault('$nodename', True)
> > > + schema['properties'].setdefault('bootph-pre-sram', True)
> > > + schema['properties'].setdefault('bootph-verify', True)
> > > + schema['properties'].setdefault('bootph-pre-ram', True)
> > > + schema['properties'].setdefault('bootph-some-ram', True)
> > > + schema['properties'].setdefault('bootph-all', True)
> > >
> > > keys = list()
> > > if 'properties' in schema:
> > > diff --git a/dtschema/schemas/bootph.yaml b/dtschema/schemas/bootph.yaml
> > > new file mode 100644
> > > index 0000000..275c4da
> > > --- /dev/null
> > > +++ b/dtschema/schemas/bootph.yaml
> > > @@ -0,0 +1,86 @@
> > > +# SPDX-License-Identifier: BSD-2-Clause
> > > +# Copyright 2022 Google LLC
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/bootph.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Boot-phase-specific device nodes
> > > +
> > > +maintainers:
> > > + - Simon Glass <sjg@xxxxxxxxxxxx>
> > > +
> > > +description: |
> > > + Some programs run in memory-constrained environments yet want to make use
> > > + of device tree.
> > > +
> > > + The full device tree is often quite large relative to the available memory
> > > + of a boot phase, so cannot fit into every phase of the boot process. Even
> > > + when memory is not a problem, some phases may wish to limit which device
> > > + nodes are present, so as to reduce execution time.
> > > +
> > > + This binding supports adding tags to device tree nodes to allow them to be
> > > + marked according to the phases where they should be included.
> > > +
> > > + Without any tags, nodes are included only in the final phase, where all
> > > + memory is available. Any untagged nodes are dropped from previous phases
> > > + and are ignored before the final phase is reached.
> > > +
> > > + The build process produces a separate executable for each phase. It can
> > > + use fdtgrep to drop any nodes which are not needed for a particular build.
> > > + For example, the pre-sram build will drop any nodes which are not marked
> > > + with bootph-pre-sram or bootph-all tags.
> > > +
> > > + Note that phase builds may drop the tags, since they have served their
> > > + purpose by that point. So when looking at phase-specific device tree files
> > > + you may not see these tags.
> > > +
> > > + Multiple tags can be used in the same node.
> > > +
> > > + Tags in a child node are implied to be present in all parent nodes as well.
> > > + This is important, since some missing properties (such as "ranges", or
> > > + "compatible") can cause the child node to be ignored or incorrectly
> > > + parsed.
> > > +
> > > + That said, at present, fdtgrep applies tags only to the node they are
> > > + added to, not to any parents. This means U-Boot device tree files often
> > > + add the same tag to parent nodes, rather than relying on tooling to do
> > > + this. This is a limitation of fdtgrep and it will be addressed so that
> > > + 'Linux DTs' do not need to do this.
> > > +
> > > + The available tags are describes as properties below, in order of phase
> >
> > described
> >
> > > + execution.
> > > +
> >
> > I think your issue testing is you need a 'select: true' here. 'select'
> > is how we test whether a schema should be applied to a node. The
> > default is to use compatible or $nodename for matching. You have
> > neither, so select is false.
>
> I feel like I have the opposite problem, in that the validation is not
> actually happening, i.e. it isn't failing with something like
> bootph-pre-sramxxx or anything else I put into the node:
Right. Since you get the default 'select: false', your schema is never
used for validation.
>
> I do see this:
>
> dtc -O dtb -o test.dtb test/bootphases.dts && tools/dt-validate -m test.dtb
> test.dtb: /some-device: failed to match any schema with compatible:
> ['vendor,soc1-ip']
Adding '-s test/schemas' to dt-validate should fix that error (and
probably add schema errors).
> but even changing it into a 'cpus' node it still lets me any any
> random property I like.
ATM, I think we allow additional properties in cpus nodes. That's
something I'm working on...
Most of what's in dt-schema doesn't restrict properties present in a
node in any way other than global rules on property names and values
because dt-schema is all common schemas except for the test schemas.
Rob
