| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20250430145050.69f2e950@bootlin.com>
Date: Wed, 30 Apr 2025 14:50:50 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: David Gibson <david@...son.dropbear.id.au>, Andrew Davis <afd@...com>,
Ayush Singh <ayush@...gleboard.org>, Geert Uytterhoeven
<geert@...ux-m68k.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
<krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Herve Codina
<herve.codina@...tlin.com>, Arnd Bergmann <arnd@...db.de>, Greg
Kroah-Hartman <gregkh@...uxfoundation.org>, Saravana Kannan
<saravanak@...gle.com>
Cc: devicetree@...r.kernel.org, devicetree-compiler@...r.kernel.org,
linux-kernel@...r.kernel.org, Luca Ceresoli <luca.ceresoli@...tlin.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 0/7] of: overlay: Add support for export-symbols node
feature
Hi all,
Sorry, this should be a v2 series.
I resend as v2.
Please ighnore this one.
Best regards,
Hervé
On Wed, 30 Apr 2025 14:48:59 +0200
Herve Codina <herve.codina@...tlin.com> wrote:
> Hi,
>
> At Linux Plumbers Conference 2024, we (me and Luca Ceresolli) talked
> about issues we have with runtime hotplug on non-discoverable busses
> with device tree overlays [1].
>
> On our system, a base board has a connector and addon boards can be
> connected to this connector. Both boards are described using device
> tree. The base board is described by a base device tree and addon boards
> are describe by overlays device tree. More details can be found at [2].
>
> This kind of use case can be found also on:
> - Grove Sunlight Sensor [3]
> - mikroBUS [4]
>
> One of the issue we were facing on was referencing resources available
> on the base board device tree from the addon overlay device tree.
>
> Using a nexus node [5] helps decoupling resources and avoid the
> knowledge of the full base board from the overlay. Indeed, with nexus
> node, the overlay need to know only about the nexus node itself.
>
> For instance, suppose a connector where a GPIO is connected at PinA. On
> the base board this GPIO is connected to the GPIO 12 of the SoC GPIO
> controller.
>
> The base board can describe this GPIO using a nexus node:
> soc_gpio: gpio-controller {
> #gpio-cells = <2>;
> };
>
> connector1: connector1 {
> /*
> * Nexus node for the GPIO available on the connector.
> * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
> * controller
> */
> #gpio-cells = <2>;
> gpio-map = <0 0 &soc_gpio 12 0>;
> gpio-map-mask = <0xf 0x0>;
> gpio-map-pass-thru = <0x0 0xf>;
> };
>
> The connector pin A GPIO can be referenced using:
> <&connector1 0 GPIO_ACTIVE_HIGH>
>
> This implies that the overlay needs to know about exact label that
> references the connector. This label can be different on a different
> board and so applying the overlay could failed even if it is used to
> describe the exact same addon board. Further more, a given base board
> can have several connectors where the exact same addon board can be
> connected. In that case, the same overlay cannot be used on both
> connector. Indeed, the connector labels have to be different.
>
> The export-symbols node introduced by this current series solves this
> issue.
>
> The idea of export-symbols is to have something similar to the global
> __symbols__ node but local to a specific node. Symbols listed in this
> export-symbols are local and visible only when an overlay is applied on
> a node having an export-symbols subnode.
>
> Using export-symbols, our example becomes:
> soc_gpio: gpio-controller {
> #gpio-cells = <2>;
> };
>
> connector1: connector1 {
> /*
> * Nexus node for the GPIO available on the connector.
> * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
> * controller
> */
> #gpio-cells = <2>;
> gpio-map = <0 0 &soc_gpio 12 0>;
> gpio-map-mask = <0xf 0x0>;
> gpio-map-pass-thru = <0x0 0xf>;
>
> export-symbols {
> connector = <&connector1>;
> };
> };
>
> With that export-symbols node, an overlay applied on connector1 node can
> have the symbol named 'connector' resolved to connector1. Indeed, the
> export-symbols node available at connector1 node is used when the
> overlay is applied. If the overlay has an unresolved 'connector' symbol,
> it will be resolved to connector1 thanks to export-symbols.
>
> Our overlay using the nexus node can contains:
> node {
> foo-gpio = <&connector 0 GPIO_ACTIVE_HIGH>;
> };
> It used the GPIO 0 from the connector it is applied on.
>
> A board with two connectors can be described with:
> connector1: connector1 {
> ...
> export-symbols {
> connector = <&connector1>;
> };
> };
>
> connector2: connector2 {
> ...
> export-symbols {
> connector = <&connector2>;
> };
> };
>
> In that case, the same overlay with unresolved 'connector' symbol can be
> applied on both connectors and the correct symbol resolution (connector1
> or connector2) will be done.
>
> This current series add support for the export-symbols node feature:
> - Patch 1 describes the export-symbols binding
> - Patches 2 to 6 prepare and add the support for the export-symbols
> feature
> - Patch 7 adds an unittest for the export-symbols feature
>
> Compare to the previous iteration, the series has been rebased on
> top of v6.15-rc1 and an compilation issue in unittest has been fixed.
>
> Also it is worth noting the work already done by Ayush Singh related to
> this topic on other repositories:
> - Add export-symbols in device-tree specification
> [PATCH v3] Add new `export-symbols` node [6]
>
> - Support for export-symbols in the device tree compiler
> [PATCH 0/3] Allow specifying target node in fdtoverlay [7]
> [PATCH] checks: Add support for export-symbols [8]
>
> Best regards,
> Hervé
>
> [1] https://lpc.events/event/18/contributions/1696/
> [2] https://lore.kernel.org/lkml/20240917-hotplug-drm-bridge-v4-0-bc4dfee61be6@bootlin.com/
> [3] https://lore.kernel.org/lkml/20240702164403.29067-1-afd@ti.com/
> [4] https://lore.kernel.org/lkml/20240627-mikrobus-scratch-spi-v5-0-9e6c148bf5f0@beagleboard.org/
> [5] https://github.com/devicetree-org/devicetree-specification/blob/v0.4/source/chapter2-devicetree-basics.rst#nexus-nodes-and-specifier-mapping
> [6] https://lore.kernel.org/all/20250411-export-symbols-v3-1-f59368d97063@beagleboard.org/
> [7] https://lore.kernel.org/all/20250313-fdtoverlay-target-v1-0-dd5924e12bd3@beagleboard.org/
> [8] https://lore.kernel.org/all/20250110-export-symbols-v1-1-b6213fcd6c82@beagleboard.org/
>
> Changes v1 -> v2
> v1: https://lore.kernel.org/all/20241209151830.95723-1-herve.codina@bootlin.com/
>
> - All patches
> Add 'Tested-by: Ayush Singh <ayush@...gleboard.org>'
>
> - Patch 1
> Update the 'patternProperties' regexp
>
> - Patch 2 and 4
> Fix conflicts due to the rebase on top of v6.15-rc1
>
> - Patch 5
> Fix a typo in commit log
>
> - Patch 7
> Fix a compilation issue detected by a kernel test robot
>
> Herve Codina (7):
> dt-bindings: Add support for export-symbols node
> of: resolver: Introduce get_phandle_from_symbols_node()
> of: resolver: Add export_symbols in of_resolve_phandles() parameters
> of: resolver: Add support for the export symbols node
> of: overlay: Add export_symbols_name in of_overlay_fdt_apply()
> parameters
> of: overlay: Add support for the export symbols node
> of: unittest: Add tests for export symbols
>
> .../devicetree/bindings/export-symbols.yaml | 43 +++++++++++
> drivers/misc/lan966x_pci.c | 3 +-
> drivers/of/of_kunit_helpers.c | 2 +-
> drivers/of/of_private.h | 2 +-
> drivers/of/overlay.c | 30 +++++++-
> drivers/of/resolver.c | 75 ++++++++++++++----
> drivers/of/unittest-data/Makefile | 5 ++
> .../unittest-data/overlay_export_symbols.dtso | 15 ++++
> .../of/unittest-data/testcases_common.dtsi | 1 +
> .../unittest-data/tests-export-symbols.dtsi | 30 ++++++++
> drivers/of/unittest.c | 77 +++++++++++++++++--
> include/linux/of.h | 6 +-
> 12 files changed, 258 insertions(+), 31 deletions(-)
> create mode 100644 Documentation/devicetree/bindings/export-symbols.yaml
> create mode 100644 drivers/of/unittest-data/overlay_export_symbols.dtso
> create mode 100644 drivers/of/unittest-data/tests-export-symbols.dtsi
>
--
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
Powered by blists - more mailing lists