mbox series

[v3,0/4] Add post-init-providers binding to improve suspend/resume stability

Message ID 20240221233026.2915061-1-saravanak@google.com
Headers
Series Add post-init-providers binding to improve suspend/resume stability |

Message

Saravana Kannan Feb. 21, 2024, 11:30 p.m. UTC 
  This patch series adds a "post-init-providers" device tree binding that
can be used to break dependency cycles in device tree and enforce a more
determinstic probe/suspend/resume order. This will also improve the
stability of global async probing and async suspend/resume and allow us
to enable them more easily. Yet another step away from playing initcall
chicken with probing and step towards fully async probing and
suspend/resume.

Patch 3 (the binding documentation) provides a lot more details and
examples.

v2->v3:
- Changes doc/code from "post-init-supplier" to "post-init-providers"
- Fixed some wording that was ambiguous for Conor.
- Fixed indentation, additionalProperties and white space issues in the
  yaml syntax.
- Fixed syntax errors in the example.

v1->v2:
- Addressed Documentation/commit text errors pointed out by Rob
- Reordered MAINTAINERS chunk as pointed out by Krzysztof

Saravana Kannan (4):
  driver core: Adds flags param to fwnode_link_add()
  driver core: Add FWLINK_FLAG_IGNORE to completely ignore a fwnode link
  dt-bindings: Add post-init-providers property
  of: property: fw_devlink: Add support for "post-init-providers"
    property

 .../bindings/post-init-providers.yaml         | 105 ++++++++++++++++++
 MAINTAINERS                                   |  13 ++-
 drivers/base/core.c                           |  14 ++-
 drivers/firmware/efi/sysfb_efi.c              |   2 +-
 drivers/of/property.c                         |  17 ++-
 include/linux/fwnode.h                        |   5 +-
 6 files changed, 142 insertions(+), 14 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/post-init-providers.yaml

Comments

Andy Shevchenko Feb. 22, 2024, 1:34 p.m. UTC | #1 
On Wed, Feb 21, 2024 at 03:30:20PM -0800, Saravana Kannan wrote:
> This patch series adds a "post-init-providers" device tree binding that
> can be used to break dependency cycles in device tree and enforce a more
> determinstic probe/suspend/resume order. This will also improve the
> stability of global async probing and async suspend/resume and allow us
> to enable them more easily. Yet another step away from playing initcall
> chicken with probing and step towards fully async probing and
> suspend/resume.

Do you know what is the state of affairs in ACPI? Is there any (similar)
issue even possible?
Saravana Kannan Feb. 23, 2024, 12:02 a.m. UTC | #2 
On Thu, Feb 22, 2024 at 5:34 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Wed, Feb 21, 2024 at 03:30:20PM -0800, Saravana Kannan wrote:
> > This patch series adds a "post-init-providers" device tree binding that
> > can be used to break dependency cycles in device tree and enforce a more
> > determinstic probe/suspend/resume order. This will also improve the
> > stability of global async probing and async suspend/resume and allow us
> > to enable them more easily. Yet another step away from playing initcall
> > chicken with probing and step towards fully async probing and
> > suspend/resume.
>
> Do you know what is the state of affairs in ACPI? Is there any (similar)
> issue even possible?

I'm not very familiar with ACPI, but I wouldn't be surprised if ACPI
devices have cyclic dependencies. But then ACPI on a PC doesn't
typically have as many devices/drivers and ACPI might be hiding the
dependencies from the kernel. So maybe the possibility of a cycle
visible to the kernel might be low.

I would really like to see fw_devlink extended to ACPI (it's written
in a way to make that possible), but don't have enough knowledge to do
it.

-Saravana
Rafael J. Wysocki Feb. 29, 2024, 6:01 p.m. UTC | #3 
On Fri, Feb 23, 2024 at 1:03 AM Saravana Kannan <saravanak@google.com> wrote:
>
> On Thu, Feb 22, 2024 at 5:34 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> >
> > On Wed, Feb 21, 2024 at 03:30:20PM -0800, Saravana Kannan wrote:
> > > This patch series adds a "post-init-providers" device tree binding that
> > > can be used to break dependency cycles in device tree and enforce a more
> > > determinstic probe/suspend/resume order. This will also improve the
> > > stability of global async probing and async suspend/resume and allow us
> > > to enable them more easily. Yet another step away from playing initcall
> > > chicken with probing and step towards fully async probing and
> > > suspend/resume.
> >
> > Do you know what is the state of affairs in ACPI? Is there any (similar)
> > issue even possible?
>
> I'm not very familiar with ACPI, but I wouldn't be surprised if ACPI
> devices have cyclic dependencies. But then ACPI on a PC doesn't
> typically have as many devices/drivers and ACPI might be hiding the
> dependencies from the kernel. So maybe the possibility of a cycle
> visible to the kernel might be low.
>
> I would really like to see fw_devlink extended to ACPI (it's written
> in a way to make that possible), but don't have enough knowledge to do
> it.

This might happen one day, for example in the _DEP handling context
(for now it is very limited, but I'm not actually sure how much more
capable it needs to be).

I don't think that ACPI will ever need device links between parents
and children, though.

On a related note, RISC-V people seem to want to use it on ACPI
systems for interrupt controller dependency tracking.