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.
> +properties:
> + bootph-pre-sram:
> + type: boolean
> + description: |
Don't need '|' unless you want to preserve line endings.
Otherwise, looks good. Send a PR.
> + Enable this node when SRAM is not available. This phase must set up
> + some SRAM or cache-as-RAM so it can obtain data/BSS space to use
> + during execution.
> +
> + bootph-verify:
> + type: boolean
> + description: |
> + Enable this node in the verification step, which decides which of the
> + available images should be run next.
> +
> + bootph-pre-ram:
> + type: boolean
> + description: |
> + Enable this node in the phase that sets up SDRAM.
> +
> + bootph-some-ram:
> + type: boolean
> + description: |
> + Enable this node in the phase that is run after SDRAM is working but
> + before all of it is available. Some RAM is available but it is limited
> + (e.g. it may be split into two pieces by the location of the running
> + program) because the program code is not yet relocated out of the way.
> +
> + bootph-all:
> + type: boolean
> + description: |
> + Include this node in all phases (for U-Boot see enum u_boot_phase).
> +
> +additionalProperties: true
> diff --git a/test/bootphases.dts b/test/bootphases.dts
> new file mode 100644
> index 0000000..037c626
> --- /dev/null
> +++ b/test/bootphases.dts
> @@ -0,0 +1,22 @@
> +// SPDX-License-Identifier: BSD-2-Clause
> +// Copyright 2022 Google LLC
> +
> +// An attempt to provide a device tree to validate the phase properties
> +
> +// dtc -O dtb -o test.dtb test/bootphases.dts && tools/dt-validate test.dtb
> +
> +
> +/dts-v1/;
> +
> +/ {
> + model = "none";
> + compatible = "foo";
> +
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + some-device {
> + compatible = "vendor,soc1-ip";
> + bootph-pre-sram;
> + };
> +};
> --
> 2.39.0.314.g84b9a713c41-goog
>
