| Message ID | 20230530-multiple-whooping-ee5706fceb67@wendy (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] Documentation/process: add soc maintainer handbook | expand |
Conor Dooley <conor.dooley@microchip.com> writes: > Arnd suggested that adding a maintainer handbook for the SoC "subsystem" > would be helpful in trying to bring on board maintainers for the various > new platforms cropping up in RISC-V land. > > Add a document briefly describing the role of the SoC subsystem and some > basic advice for (new) platform maintainers. > > Suggested-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com> > --- > Changes in v2: > - add Krzysztof's suggested method for avoiding inter-branch > dependencies > - explicitly mention that tags should be signed > - link to the devicetree abi document, rather than trying to explain it > here & reword that whole section > - fix some typos, capitalisation & unify bullet style > > The devicetree abi doc feels quite out of date at this point, and could > probably do with a spring clean - but it also feels like hallowed ground > on which one should tread lightly, so I won't go near that til Rob is > back. So, this is a nit, but worth considering... > Documentation/devicetree/bindings/ABI.rst | 2 + > .../devicetree/bindings/writing-schema.rst | 2 + > .../process/maintainer-handbooks.rst | 3 +- > Documentation/process/maintainer-soc.rst | 178 ++++++++++++++++++ > MAINTAINERS | 1 + > 5 files changed, 185 insertions(+), 1 deletion(-) > create mode 100644 Documentation/process/maintainer-soc.rst > > diff --git a/Documentation/devicetree/bindings/ABI.rst b/Documentation/devicetree/bindings/ABI.rst > index a885713cf184..93ec82f78ae5 100644 > --- a/Documentation/devicetree/bindings/ABI.rst > +++ b/Documentation/devicetree/bindings/ABI.rst > @@ -1,5 +1,7 @@ > .. SPDX-License-Identifier: GPL-2.0 > > +.. _devicetree-abi: Somehow we've developed this habit of putting labels at the top of each file; I really think that they just add clutter and are best left out. Without the label, this reference: > +Perhaps one of the most important things to highlight is that dt-bindings > +document the ABI between the devicetree and the kernel. Please see > +:ref:`devicetree-abi` more information on the ABI. ...can just be written as "Please see Documentation/devicetree/bindings/ABI.rst". The cross-reference link will be generated as expected, and readers of the plain-text docs don't have to go grepping to find the reference. Thanks, jon
On Tue, May 30, 2023 at 07:02:26AM -0600, Jonathan Corbet wrote: > Conor Dooley <conor.dooley@microchip.com> writes: > > diff --git a/Documentation/devicetree/bindings/ABI.rst b/Documentation/devicetree/bindings/ABI.rst > > index a885713cf184..93ec82f78ae5 100644 > > --- a/Documentation/devicetree/bindings/ABI.rst > > +++ b/Documentation/devicetree/bindings/ABI.rst > > @@ -1,5 +1,7 @@ > > .. SPDX-License-Identifier: GPL-2.0 > > > > +.. _devicetree-abi: > > Somehow we've developed this habit of putting labels at the top of each > file; I really think that they just add clutter and are best left out. > Without the label, this reference: > > > +Perhaps one of the most important things to highlight is that dt-bindings > > +document the ABI between the devicetree and the kernel. Please see > > +:ref:`devicetree-abi` more information on the ABI. > > ...can just be written as "Please see > Documentation/devicetree/bindings/ABI.rst". The cross-reference link > will be generated as expected, and readers of the plain-text docs don't > have to go grepping to find the reference. Sure. As someone who does read these things in their editor that sounds preferable to me. I didn't know that I could do that, as the whole "building the docs" thing is new to me ;) I'll wait a bit before resubmitting for obvious reasons. Cheers, Conor.
On 30/05/2023 14:49, Conor Dooley wrote: > Arnd suggested that adding a maintainer handbook for the SoC "subsystem" > would be helpful in trying to bring on board maintainers for the various > new platforms cropping up in RISC-V land. > > Add a document briefly describing the role of the SoC subsystem and some > basic advice for (new) platform maintainers. > > Suggested-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com> > --- > Changes in v2: > - add Krzysztof's suggested method for avoiding inter-branch > dependencies > - explicitly mention that tags should be signed > - link to the devicetree abi document, rather than trying to explain it > here & reword that whole section > - fix some typos, capitalisation & unify bullet style > > The devicetree abi doc feels quite out of date at this point, and could > probably do with a spring clean - but it also feels like hallowed groun Yep, but that's another topic. > d > on which one should tread lightly, so I won't go near that til Rob is > back. Thanks! Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Best regards, Krzysztof
On 5/30/23 05:49, Conor Dooley wrote: > Arnd suggested that adding a maintainer handbook for the SoC "subsystem" > would be helpful in trying to bring on board maintainers for the various > new platforms cropping up in RISC-V land. > > Add a document briefly describing the role of the SoC subsystem and some > basic advice for (new) platform maintainers. > > Suggested-by: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com> > --- > Changes in v2: > - add Krzysztof's suggested method for avoiding inter-branch > dependencies > - explicitly mention that tags should be signed > - link to the devicetree abi document, rather than trying to explain it > here & reword that whole section > - fix some typos, capitalisation & unify bullet style > > The devicetree abi doc feels quite out of date at this point, and could > probably do with a spring clean - but it also feels like hallowed ground > on which one should tread lightly, so I won't go near that til Rob is > back. > --- > Documentation/devicetree/bindings/ABI.rst | 2 + > .../devicetree/bindings/writing-schema.rst | 2 + > .../process/maintainer-handbooks.rst | 3 +- > Documentation/process/maintainer-soc.rst | 178 ++++++++++++++++++ > MAINTAINERS | 1 + > 5 files changed, 185 insertions(+), 1 deletion(-) > create mode 100644 Documentation/process/maintainer-soc.rst > > diff --git a/Documentation/devicetree/bindings/ABI.rst b/Documentation/devicetree/bindings/ABI.rst > index a885713cf184..93ec82f78ae5 100644 > --- a/Documentation/devicetree/bindings/ABI.rst > +++ b/Documentation/devicetree/bindings/ABI.rst > @@ -1,5 +1,7 @@ > .. SPDX-License-Identifier: GPL-2.0 > > +.. _devicetree-abi: > + > =================== > Devicetree (DT) ABI > =================== > diff --git a/Documentation/devicetree/bindings/writing-schema.rst b/Documentation/devicetree/bindings/writing-schema.rst > index 4a381d20f2b4..640d857dabf3 100644 > --- a/Documentation/devicetree/bindings/writing-schema.rst > +++ b/Documentation/devicetree/bindings/writing-schema.rst > @@ -136,6 +136,8 @@ installed. Ensure they are in your PATH (~/.local/bin by default). > > Recommended is also to install yamllint (used by dtschema when present). I don't see anything in Documentation/ about where to find yamllint... please. > > +.. _running-checks: > + > Running checks > ~~~~~~~~~~~~~~ > > diff --git a/Documentation/process/maintainer-soc.rst b/Documentation/process/maintainer-soc.rst > new file mode 100644 > index 000000000000..9683c7d199b2 > --- /dev/null > +++ b/Documentation/process/maintainer-soc.rst > @@ -0,0 +1,178 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +.. _maintainer-soc: > + > +============= > +SoC Subsystem > +============= > + > +Overview > +-------- > + > +The SoC subsystem is a place of aggregation for SoC-specific code. > +The main components of the subsystem are: > + > +* devicetrees for 32- & 64-bit ARM and RISC-V > +* 32-bit ARM board files (arch/arm/mach*) > +* 32- & 64-bit ARM defconfigs > +* SoC specific drivers across architectures, in particular for 32- & 64-bit SoC-specific > + ARM, RISC-V and Loongarch > + > +These "SoC specific drivers" do not include clock, GPIO etc drivers that have SoC-specific GPIO, etc. drivers that have > +other top-level maintainers. The drivers/soc/ directory is generally meant > +for kernel-internal drivers that are used by other drivers to provide SoC SoC- > +specific functionality like identifying a SoC revision or interfacing with I would write: an SoC > +power domains. > + > +The SoC subsystem also serves as an intermediate location for changes to > +drivers/bus, drivers/firmware, drivers/reset and drivers/memory. The addition > +of new platforms, or the removal of existing ones, often go through the SoC > +tree as a dedicated branch covering multiple subsystems. > + > +The main SoC tree is housed on git.kernel.org: > + https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git/ > + > +Clearly this is quite a wide range of topics, which no one person, or even > +small group of people are capable of maintaining. Instead, the SoC subsystem > +is comprised of many submaintainers, each taking care of individual platforms > +and driver sub-directories. submaintainers and sub-directories ? hm. > +In this regard, "platform" usually refers to a series of SoCs from a given > +vendor, for example, Nvidia's series of Tegra SoCs. Many submaintainers operate > +on a vendor level, responsible for multiple product lines. For several reasons, > +including acquisitions/different business units in a company, things vary > +significantly here. The various submaintainers are documented in the > +MAINTAINERS file. > + > +Most of these submaintainers have their own trees where they stage patches, > +sending pull requests to the main SoC tree. These trees are usually, but not > +always, listed in MAINTAINERS. The main SoC maintainers can be reached via the > +alias soc@kernel.org if there is no platform-specific maintainer, or if they > +are unresponsive. > + > +What the SoC tree is not, however, is a location for architecture specific code architecture-specific > +changes. Each architecture has it's own maintainers that are responsible for its > +architectural details, cpu errata and the like. CPU > + > +Information for (new) Submaintainers > +------------------------------------ > + > +As new platforms spring up, they often bring with them new submaintainers, > +many of whom work for the silicon vendor, and may not be familiar with the > +process. > + > +Devicetree ABI Stability > +~~~~~~~~~~~~~~~~~~~~~~~~ > + > +Perhaps one of the most important things to highlight is that dt-bindings > +document the ABI between the devicetree and the kernel. Please see > +:ref:`devicetree-abi` more information on the ABI. > + > +If changes are being made to a devicetree that are incompatible with old > +kernels, the devicetree patch should not be applied until the driver is, or an > +appropriate time later. Most importantly, any incompatible changes should be > +clearly pointed out in the patch description and pull request, along with the > +expected impact on existing users, such as bootloaders or other operating > +systems. > + > +Driver Branch Dependencies > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +A common problem is synchronizing changes between device drivers and devicetree > +files, even if a change is compatible in both directions, this may require files. Even if > +coordinating how the changes get merged through different maintainer trees. > + > +Usually the branch that includes a driver change will also include the > +corresponding change to the devicetree binding description, to ensure they are > +in fact compatible. This means that the devicetree branch can end up causing s/in fact/remain/ (suggestion) > +warnings in the "make dtbs_check" step. If a devicetree change depends on > +missing additions to a header file in include/dt-bindings/, it will fail the > +"make dtbs" step and not get merged. > + > +There are multiple ways to deal with this: > + > +* Avoid defining custom macros in include/dt-bindings/ for hardware constants > + that can be derived from a datasheet -- binding macros in header file should in a header file | in header files > + only be used as a last resort if there is no natural way to define a binding > + > +* Use literal values in the devicetree file in place of macros even when a > + header is required, and change them to the named representation in a > + following release > + > +* Defer the devicetree changes to a release after the binding and driver have > + already been merged > + > +* Change the bindings in a shared immutable branch that is used as the base for > + both the driver change and the devicetree changes > + > +* Add duplicate defines in the devicetree file guarded by an #ifndef section, > + removing them in a later release > + > +Devicetree Naming Convention > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +The general naming scheme for devicetree files are as follows. The aspects of a scheme ... is > +platform that are set at the SoC level, like cpu cores, are contained in a file CPU > +named $soc.dtsi, for example, jh7100.dtsi. Integration details, that will vary > +from board to board, are described in $soc-$board.dtsi. An example of this is > +jh7100-beaglev-starlight.dts. Often many boards are variations on a theme, and ^^^ Why not dtsi, like the sentence before says? or is the $soc-$board.dtsi wrong? > +frequently there are intermediate files, such as jh7100-common.dtsi, which sit > +between the $soc.dtsi and $soc-$board.dts files, containing the descriptions of > +common hardware. > + > +Some platforms also have System on Modules, containing an SoC, which are then > +integrated into several different boards. For these platforms, $soc-$som.dtsi > +and $soc-$som-$board.dts are typical. > + > +Directories are usually named after the vendor of the SoC at the time of it's its > +inclusion, leading to some historical directory names in the tree. > + > +Validating Devicetree Files > +~~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +``make dtbs_check`` can be used to validate that devicetree files are compliant > +with the dt-bindings that describe the ABI. Please see :ref:`running-checks` > +for more information on the validation of devicetrees. > + > +For new platforms, or additions to existing ones, ``make dtbs_check`` should not > +add any new warnings. For RISC-V, as it has the advantage of being a newer > +architecture, ``make dtbs_check W=1`` is required to not add any new warnings. > +If in any doubt about a devicetree change, reach out to the devicetree > +maintainers. > + > +Branches and Pull Requests > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +Just as the main SoC tree has several branches, it is expected that > +submaintainers will do the same. Driver, defconfig and devicetree changes should > +all be split into separate branches and appear in separate pull requests to the > +SoC maintainers. Each branch should be usable by itself and avoid > +regressions that originate from dependencies on other branches. > + > +Small sets of patches can also be sent as separate emails to soc@kernel.org, > +grouped into the same categories. > + > +If changes do not fit into the normal patterns, there can be additional > +top-level branches, e.g. for a treewide rework, or the addition of new SoC > +platforms including dts files and drivers. > + > +Branches with a lot of changes can benefit from getting split up into separate > +topics branches, even if they end up getting merged into the same branch of the > +SoC tree. An example here would be one branch for devicetree warning fixes, one > +for a rework and one for newly added boards. > + > +Another common way to split up changes is to send an early pull request with the > +majority of the changes at some point between rc1 and rc4, following up with one > +or more smaller pull requests towards the end of the cycle that can add late > +changes or address problems idenfied while testing the first set. identified > + > +While there is no cut-off time for late pull requests, it helps to only send > +small branches as time gets closer to the merge window. > + > +Pull requests for bugfixes for the current release can be sent at any time, but > +again having multiple smaller branches is better than trying to combine too many > +patches into one pull request. > + > +The subject line of a pull request should begin with "[GIT PULL]" and made using > +a signed tag, rather than a branch. This tag should contain a short description > +summarising the changes in the pull request. For more detail on sending pull > +requests, please see :ref:`pullrequests`. >
Hey Randy, On Tue, May 30, 2023 at 08:28:44AM -0700, Randy Dunlap wrote: > On 5/30/23 05:49, Conor Dooley wrote: > > Recommended is also to install yamllint (used by dtschema when present). > > I don't see anything in Documentation/ about where to find yamllint... > please. Sounds like an unrelated fix to me ;) > submaintainers and sub-directories ? hm. I had sub-maintainers before being asked to change! I think that subdirectories is correct though & the hyphenated form is incorrect. > > +named $soc.dtsi, for example, jh7100.dtsi. Integration details, that will vary > > +from board to board, are described in $soc-$board.dtsi. An example of this is > > +jh7100-beaglev-starlight.dts. Often many boards are variations on a theme, and > > ^^^ Why not dtsi, like the sentence before says? > or is the $soc-$board.dtsi wrong? $soc-$board.dtsi is wrong. > > +Another common way to split up changes is to send an early pull request with the > > +majority of the changes at some point between rc1 and rc4, following up with one > > +or more smaller pull requests towards the end of the cycle that can add late > > +changes or address problems idenfied while testing the first set. > > identified Surprised nvim didn't whinge about that one. Thanks for pointing out the wee mistakes all over the place, Conor.
On Tue, May 30, 2023 at 01:49:36PM +0100, Conor Dooley wrote: > diff --git a/Documentation/process/maintainer-soc.rst b/Documentation/process/maintainer-soc.rst > new file mode 100644 > index 000000000000..9683c7d199b2 > --- /dev/null > +++ b/Documentation/process/maintainer-soc.rst > @@ -0,0 +1,178 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +.. _maintainer-soc: > + > +============= > +SoC Subsystem > +============= > + > +Overview > +-------- > + > +The SoC subsystem is a place of aggregation for SoC-specific code. > +The main components of the subsystem are: > + > +* devicetrees for 32- & 64-bit ARM and RISC-V > +* 32-bit ARM board files (arch/arm/mach*) > +* 32- & 64-bit ARM defconfigs > +* SoC specific drivers across architectures, in particular for 32- & 64-bit > + ARM, RISC-V and Loongarch > + > +These "SoC specific drivers" do not include clock, GPIO etc drivers that have > +other top-level maintainers. The drivers/soc/ directory is generally meant > +for kernel-internal drivers that are used by other drivers to provide SoC > +specific functionality like identifying a SoC revision or interfacing with > +power domains. > + > +The SoC subsystem also serves as an intermediate location for changes to > +drivers/bus, drivers/firmware, drivers/reset and drivers/memory. The addition > +of new platforms, or the removal of existing ones, often go through the SoC > +tree as a dedicated branch covering multiple subsystems. > + > +The main SoC tree is housed on git.kernel.org: > + https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git/ > + > +Clearly this is quite a wide range of topics, which no one person, or even > +small group of people are capable of maintaining. Instead, the SoC subsystem > +is comprised of many submaintainers, each taking care of individual platforms > +and driver sub-directories. > +In this regard, "platform" usually refers to a series of SoCs from a given > +vendor, for example, Nvidia's series of Tegra SoCs. Many submaintainers operate > +on a vendor level, responsible for multiple product lines. For several reasons, > +including acquisitions/different business units in a company, things vary > +significantly here. The various submaintainers are documented in the > +MAINTAINERS file. > + > +Most of these submaintainers have their own trees where they stage patches, > +sending pull requests to the main SoC tree. These trees are usually, but not > +always, listed in MAINTAINERS. The main SoC maintainers can be reached via the > +alias soc@kernel.org if there is no platform-specific maintainer, or if they > +are unresponsive. > + > +What the SoC tree is not, however, is a location for architecture specific code > +changes. Each architecture has it's own maintainers that are responsible for > +architectural details, cpu errata and the like. > + > +Information for (new) Submaintainers > +------------------------------------ > + > +As new platforms spring up, they often bring with them new submaintainers, > +many of whom work for the silicon vendor, and may not be familiar with the > +process. > + > +Devicetree ABI Stability > +~~~~~~~~~~~~~~~~~~~~~~~~ > + > +Perhaps one of the most important things to highlight is that dt-bindings > +document the ABI between the devicetree and the kernel. Please see > +:ref:`devicetree-abi` more information on the ABI. > + > +If changes are being made to a devicetree that are incompatible with old > +kernels, the devicetree patch should not be applied until the driver is, or an Until the incompatible driver changes are merged? > +appropriate time later. Most importantly, any incompatible changes should be > +clearly pointed out in the patch description and pull request, along with the > +expected impact on existing users, such as bootloaders or other operating > +systems. > + > +Driver Branch Dependencies > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +A common problem is synchronizing changes between device drivers and devicetree > +files, even if a change is compatible in both directions, this may require > +coordinating how the changes get merged through different maintainer trees. > + > +Usually the branch that includes a driver change will also include the > +corresponding change to the devicetree binding description, to ensure they are > +in fact compatible. This means that the devicetree branch can end up causing > +warnings in the "make dtbs_check" step. If a devicetree change depends on > +missing additions to a header file in include/dt-bindings/, it will fail the > +"make dtbs" step and not get merged. Sounds like passing `make dtbs` is a merging requirement. > +Pull requests for bugfixes for the current release can be sent at any time, but > +again having multiple smaller branches is better than trying to combine too many > +patches into one pull request. > + > +The subject line of a pull request should begin with "[GIT PULL]" and made using > +a signed tag, rather than a branch. This tag should contain a short description > +summarising the changes in the pull request. For more detail on sending pull > +requests, please see :ref:`pullrequests`. As jon had said, I simply prefer to write the last cross-ref as: ``` ... For more details on sending pull requests, see Documentation/maintainer/pull-requests.rst. ``` Thanks.
On 31/05/2023 08:30, Bagas Sanjaya wrote: >> +appropriate time later. Most importantly, any incompatible changes should be >> +clearly pointed out in the patch description and pull request, along with the >> +expected impact on existing users, such as bootloaders or other operating >> +systems. >> + >> +Driver Branch Dependencies >> +~~~~~~~~~~~~~~~~~~~~~~~~~~ >> + >> +A common problem is synchronizing changes between device drivers and devicetree >> +files, even if a change is compatible in both directions, this may require >> +coordinating how the changes get merged through different maintainer trees. >> + >> +Usually the branch that includes a driver change will also include the >> +corresponding change to the devicetree binding description, to ensure they are >> +in fact compatible. This means that the devicetree branch can end up causing >> +warnings in the "make dtbs_check" step. If a devicetree change depends on >> +missing additions to a header file in include/dt-bindings/, it will fail the >> +"make dtbs" step and not get merged. > > Sounds like passing `make dtbs` is a merging requirement. And why shouldn't be? Best regards, Krzysztof
On Wed, May 31, 2023 at 01:30:07PM +0700, Bagas Sanjaya wrote: > On Tue, May 30, 2023 at 01:49:36PM +0100, Conor Dooley wrote: > > +If changes are being made to a devicetree that are incompatible with old > > +kernels, the devicetree patch should not be applied until the driver is, or an > Until the incompatible driver changes are merged? Yeah, could probably do with a bit of rework here. > > +appropriate time later. Most importantly, any incompatible changes should be > > +clearly pointed out in the patch description and pull request, along with the > > +expected impact on existing users, such as bootloaders or other operating > > +systems. > > + > > +Driver Branch Dependencies > > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > > + > > +A common problem is synchronizing changes between device drivers and devicetree > > +files, even if a change is compatible in both directions, this may require > > +coordinating how the changes get merged through different maintainer trees. > > + > > +Usually the branch that includes a driver change will also include the > > +corresponding change to the devicetree binding description, to ensure they are > > +in fact compatible. This means that the devicetree branch can end up causing > > +warnings in the "make dtbs_check" step. If a devicetree change depends on > > +missing additions to a header file in include/dt-bindings/, it will fail the > > +"make dtbs" step and not get merged. > > Sounds like passing `make dtbs` is a merging requirement. I think it goes without saying that not breaking the build is a merge requirement! Cheers, Conor.
On 5/31/23 13:51, Krzysztof Kozlowski wrote: >> Sounds like passing `make dtbs` is a merging requirement. > > And why shouldn't be? > I don't have anything more to say here...
diff --git a/Documentation/devicetree/bindings/ABI.rst b/Documentation/devicetree/bindings/ABI.rst index a885713cf184..93ec82f78ae5 100644 --- a/Documentation/devicetree/bindings/ABI.rst +++ b/Documentation/devicetree/bindings/ABI.rst @@ -1,5 +1,7 @@ .. SPDX-License-Identifier: GPL-2.0 +.. _devicetree-abi: + =================== Devicetree (DT) ABI =================== diff --git a/Documentation/devicetree/bindings/writing-schema.rst b/Documentation/devicetree/bindings/writing-schema.rst index 4a381d20f2b4..640d857dabf3 100644 --- a/Documentation/devicetree/bindings/writing-schema.rst +++ b/Documentation/devicetree/bindings/writing-schema.rst @@ -136,6 +136,8 @@ installed. Ensure they are in your PATH (~/.local/bin by default). Recommended is also to install yamllint (used by dtschema when present). +.. _running-checks: + Running checks ~~~~~~~~~~~~~~ diff --git a/Documentation/process/maintainer-handbooks.rst b/Documentation/process/maintainer-handbooks.rst index d783060b4cc6..fe24cb665fb7 100644 --- a/Documentation/process/maintainer-handbooks.rst +++ b/Documentation/process/maintainer-handbooks.rst @@ -15,5 +15,6 @@ Contents: :numbered: :maxdepth: 2 - maintainer-tip maintainer-netdev + maintainer-soc + maintainer-tip diff --git a/Documentation/process/maintainer-soc.rst b/Documentation/process/maintainer-soc.rst new file mode 100644 index 000000000000..9683c7d199b2 --- /dev/null +++ b/Documentation/process/maintainer-soc.rst @@ -0,0 +1,178 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _maintainer-soc: + +============= +SoC Subsystem +============= + +Overview +-------- + +The SoC subsystem is a place of aggregation for SoC-specific code. +The main components of the subsystem are: + +* devicetrees for 32- & 64-bit ARM and RISC-V +* 32-bit ARM board files (arch/arm/mach*) +* 32- & 64-bit ARM defconfigs +* SoC specific drivers across architectures, in particular for 32- & 64-bit + ARM, RISC-V and Loongarch + +These "SoC specific drivers" do not include clock, GPIO etc drivers that have +other top-level maintainers. The drivers/soc/ directory is generally meant +for kernel-internal drivers that are used by other drivers to provide SoC +specific functionality like identifying a SoC revision or interfacing with +power domains. + +The SoC subsystem also serves as an intermediate location for changes to +drivers/bus, drivers/firmware, drivers/reset and drivers/memory. The addition +of new platforms, or the removal of existing ones, often go through the SoC +tree as a dedicated branch covering multiple subsystems. + +The main SoC tree is housed on git.kernel.org: + https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git/ + +Clearly this is quite a wide range of topics, which no one person, or even +small group of people are capable of maintaining. Instead, the SoC subsystem +is comprised of many submaintainers, each taking care of individual platforms +and driver sub-directories. +In this regard, "platform" usually refers to a series of SoCs from a given +vendor, for example, Nvidia's series of Tegra SoCs. Many submaintainers operate +on a vendor level, responsible for multiple product lines. For several reasons, +including acquisitions/different business units in a company, things vary +significantly here. The various submaintainers are documented in the +MAINTAINERS file. + +Most of these submaintainers have their own trees where they stage patches, +sending pull requests to the main SoC tree. These trees are usually, but not +always, listed in MAINTAINERS. The main SoC maintainers can be reached via the +alias soc@kernel.org if there is no platform-specific maintainer, or if they +are unresponsive. + +What the SoC tree is not, however, is a location for architecture specific code +changes. Each architecture has it's own maintainers that are responsible for +architectural details, cpu errata and the like. + +Information for (new) Submaintainers +------------------------------------ + +As new platforms spring up, they often bring with them new submaintainers, +many of whom work for the silicon vendor, and may not be familiar with the +process. + +Devicetree ABI Stability +~~~~~~~~~~~~~~~~~~~~~~~~ + +Perhaps one of the most important things to highlight is that dt-bindings +document the ABI between the devicetree and the kernel. Please see +:ref:`devicetree-abi` more information on the ABI. + +If changes are being made to a devicetree that are incompatible with old +kernels, the devicetree patch should not be applied until the driver is, or an +appropriate time later. Most importantly, any incompatible changes should be +clearly pointed out in the patch description and pull request, along with the +expected impact on existing users, such as bootloaders or other operating +systems. + +Driver Branch Dependencies +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A common problem is synchronizing changes between device drivers and devicetree +files, even if a change is compatible in both directions, this may require +coordinating how the changes get merged through different maintainer trees. + +Usually the branch that includes a driver change will also include the +corresponding change to the devicetree binding description, to ensure they are +in fact compatible. This means that the devicetree branch can end up causing +warnings in the "make dtbs_check" step. If a devicetree change depends on +missing additions to a header file in include/dt-bindings/, it will fail the +"make dtbs" step and not get merged. + +There are multiple ways to deal with this: + +* Avoid defining custom macros in include/dt-bindings/ for hardware constants + that can be derived from a datasheet -- binding macros in header file should + only be used as a last resort if there is no natural way to define a binding + +* Use literal values in the devicetree file in place of macros even when a + header is required, and change them to the named representation in a + following release + +* Defer the devicetree changes to a release after the binding and driver have + already been merged + +* Change the bindings in a shared immutable branch that is used as the base for + both the driver change and the devicetree changes + +* Add duplicate defines in the devicetree file guarded by an #ifndef section, + removing them in a later release + +Devicetree Naming Convention +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The general naming scheme for devicetree files are as follows. The aspects of a +platform that are set at the SoC level, like cpu cores, are contained in a file +named $soc.dtsi, for example, jh7100.dtsi. Integration details, that will vary +from board to board, are described in $soc-$board.dtsi. An example of this is +jh7100-beaglev-starlight.dts. Often many boards are variations on a theme, and +frequently there are intermediate files, such as jh7100-common.dtsi, which sit +between the $soc.dtsi and $soc-$board.dts files, containing the descriptions of +common hardware. + +Some platforms also have System on Modules, containing an SoC, which are then +integrated into several different boards. For these platforms, $soc-$som.dtsi +and $soc-$som-$board.dts are typical. + +Directories are usually named after the vendor of the SoC at the time of it's +inclusion, leading to some historical directory names in the tree. + +Validating Devicetree Files +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +``make dtbs_check`` can be used to validate that devicetree files are compliant +with the dt-bindings that describe the ABI. Please see :ref:`running-checks` +for more information on the validation of devicetrees. + +For new platforms, or additions to existing ones, ``make dtbs_check`` should not +add any new warnings. For RISC-V, as it has the advantage of being a newer +architecture, ``make dtbs_check W=1`` is required to not add any new warnings. +If in any doubt about a devicetree change, reach out to the devicetree +maintainers. + +Branches and Pull Requests +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Just as the main SoC tree has several branches, it is expected that +submaintainers will do the same. Driver, defconfig and devicetree changes should +all be split into separate branches and appear in separate pull requests to the +SoC maintainers. Each branch should be usable by itself and avoid +regressions that originate from dependencies on other branches. + +Small sets of patches can also be sent as separate emails to soc@kernel.org, +grouped into the same categories. + +If changes do not fit into the normal patterns, there can be additional +top-level branches, e.g. for a treewide rework, or the addition of new SoC +platforms including dts files and drivers. + +Branches with a lot of changes can benefit from getting split up into separate +topics branches, even if they end up getting merged into the same branch of the +SoC tree. An example here would be one branch for devicetree warning fixes, one +for a rework and one for newly added boards. + +Another common way to split up changes is to send an early pull request with the +majority of the changes at some point between rc1 and rc4, following up with one +or more smaller pull requests towards the end of the cycle that can add late +changes or address problems idenfied while testing the first set. + +While there is no cut-off time for late pull requests, it helps to only send +small branches as time gets closer to the merge window. + +Pull requests for bugfixes for the current release can be sent at any time, but +again having multiple smaller branches is better than trying to combine too many +patches into one pull request. + +The subject line of a pull request should begin with "[GIT PULL]" and made using +a signed tag, rather than a branch. This tag should contain a short description +summarising the changes in the pull request. For more detail on sending pull +requests, please see :ref:`pullrequests`. diff --git a/MAINTAINERS b/MAINTAINERS index 7e0b87d5aa2e..29631c325857 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -1815,6 +1815,7 @@ L: linux-arm-kernel@lists.infradead.org (moderated for non-subscribers) S: Maintained C: irc://irc.libera.chat/armlinux T: git git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git +F: Documentation/process/maintainer-soc.rst F: arch/arm/boot/dts/Makefile F: arch/arm64/boot/dts/Makefile
Arnd suggested that adding a maintainer handbook for the SoC "subsystem" would be helpful in trying to bring on board maintainers for the various new platforms cropping up in RISC-V land. Add a document briefly describing the role of the SoC subsystem and some basic advice for (new) platform maintainers. Suggested-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Conor Dooley <conor.dooley@microchip.com> --- Changes in v2: - add Krzysztof's suggested method for avoiding inter-branch dependencies - explicitly mention that tags should be signed - link to the devicetree abi document, rather than trying to explain it here & reword that whole section - fix some typos, capitalisation & unify bullet style The devicetree abi doc feels quite out of date at this point, and could probably do with a spring clean - but it also feels like hallowed ground on which one should tread lightly, so I won't go near that til Rob is back. --- Documentation/devicetree/bindings/ABI.rst | 2 + .../devicetree/bindings/writing-schema.rst | 2 + .../process/maintainer-handbooks.rst | 3 +- Documentation/process/maintainer-soc.rst | 178 ++++++++++++++++++ MAINTAINERS | 1 + 5 files changed, 185 insertions(+), 1 deletion(-) create mode 100644 Documentation/process/maintainer-soc.rst