Hi Linus, I am noting a few grammar nits below... [and + linux-doc] On 5/5/23 05:43, Linus Walleij wrote: > This document is named "Linux and Devicetree" so I think we > should write a bit more about how the device tree fits into > the Linux kernel frameworks these days after we have created > the fwnode and swnode. > > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > --- > These docs are old and outdated and need to be edited to > reflect the current situation. > --- > ChangeLog v1->v2: > - Spelling mistakes > - Resend because nothing happens > --- > Documentation/devicetree/usage-model.rst | 45 +++++++++++++++++++++++++++++--- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/Documentation/devicetree/usage-model.rst b/Documentation/devicetree/usage-model.rst > index b6a287955ee5..37605cb549cf 100644 > --- a/Documentation/devicetree/usage-model.rst > +++ b/Documentation/devicetree/usage-model.rst > @@ -75,7 +75,44 @@ out of mainline (nios) have some level of DT support. > If you haven't already read the Device Tree Usage\ [1]_ page, > then go read it now. It's okay, I'll wait.... > > -2.1 High Level View > +2.1 Linux Kernel Firmware Abstractions > +-------------------------------------- > + > +The Linux kernel supports several different hardware description > +frameworks and DT is just one of them. The closest sibling is the > +:ref:`Documentation/firmware-guide/acpi/index.rst ACPI` > +DSDT (Differentiated System Description Table). > + > +To make it possible to write a device driver that will adapt to DT > +or other hardware description models, the kernel has grown some > +abstractions, first and foremost the firmware node API, exposing > +device properties. The firmware node "fwnode" internals can be found > +in ``<linux/fwnode.h>`` while the device driver-facing API can be > +found in ``<linux/property.h>``. The idea is that if a driver is using > +the firmware node API, it should be trivial to support DT and ACPI > +DSDT alike in the same driver. > + > +The fwnode framework also makes it possible to modify and extend the > +Linux in-kernel model with software-managed nodes "swnodes" to apply > +quirks or manage registration of devices that cannot be handled any > +other way. This API can also be found in ``<linux/property.h>``. > + > +Further, when the DT core register devices these need to fold into the core registers > +Linux device driver model, which essentially means that some kind of > +``struct device`` has to be created to match a corresponding > +``struct device_driver``. This API can be explored in > +detail in :ref:`Documentation/driver-api/driver-model/index.rst the driver API documentation` > +but what you need to know is that the Linux DT parser code will on its > +own mostly spawn platform devices and AMBA devices on the platform > +and AMBA bus respectively, and apart from that it will augment devices > +spawn on other buses where applicable. spawned > + > +Every Linux kernel subsystem that want to supply additional data to that wants > +detected devices using the device tree, or that want to provide that wants > +resources to other devices in the DT, will need to implement calls into > +the DT abstractions. > + > +2.2 High Level View > ------------------- > The most important thing to understand is that the DT is simply a data > structure that describes the hardware. There is nothing magical about > @@ -97,7 +134,7 @@ Linux uses DT data for three major purposes: > 2) runtime configuration, and > 3) device population. > > -2.2 Platform Identification > +2.3 Platform Identification > --------------------------- > First and foremost, the kernel will use data in the DT to identify the > specific machine. In a perfect world, the specific platform shouldn't > @@ -180,7 +217,7 @@ However, this approach does not take into account the priority of the > compatible list, and probably should be avoided for new architecture > support. > > -2.3 Runtime configuration > +2.4 Runtime configuration > ------------------------- > In most cases, a DT will be the sole method of communicating data from > firmware to the kernel, so also gets used to pass in runtime and > @@ -217,7 +254,7 @@ On ARM, the function setup_machine_fdt() is responsible for early > scanning of the device tree after selecting the correct machine_desc > that supports the board. > > -2.4 Device population > +2.5 Device population > --------------------- > After the board has been identified, and after the early configuration data > has been parsed, then kernel initialization can proceed in the normal > > --- > base-commit: 457391b0380335d5e9a5babdec90ac53928b23b4 > change-id: 20230505-dt-docs-refresh-515edbdbbd01 > > Best regards, For @linux-doc: Is there something in ReST that does auto section numbering so that this renumbering does not have to be repeated in the future? Thanks for the additional documentation. -- ~Randy