linux-kernel - Re: [PATCH v3 01/15] dt-bindings: remoteproc: Add bindind to support autonomous processors

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Date:   Tue, 1 Dec 2020 16:43:27 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     ohad@...ery.com, bjorn.andersson@...aro.org,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnaud.pouliquen@...com
Subject: Re: [PATCH v3 01/15] dt-bindings: remoteproc: Add bindind to support
 autonomous processors

Hi Rob,

On Mon, Nov 30, 2020 at 10:33:21AM -0700, Rob Herring wrote:
> On Thu, Nov 26, 2020 at 02:06:28PM -0700, Mathieu Poirier wrote:
> > This patch adds a binding to guide the remoteproc core on how to deal with
> > remote processors in two cases:
> > 
> > 1) When an application holding a reference to a remote processor character
> >    device interface crashes.
> > 
> > 2) when the platform driver for a remote processor is removed.
> > 
> > In both cases if "autonomous-on-core-reboot" is specified in the remote
> > processor DT node, the remoteproc core will detach the remote processor
> > rather than switching it off.
> > 
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > ---
> >  .../bindings/remoteproc/remoteproc-core.yaml  | 25 +++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/remoteproc/remoteproc-core.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/remoteproc/remoteproc-core.yaml b/Documentation/devicetree/bindings/remoteproc/remoteproc-core.yaml
> > new file mode 100644
> > index 000000000000..3032734f42a3
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/remoteproc/remoteproc-core.yaml
> > @@ -0,0 +1,25 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: "http://devicetree.org/schemas/remoteproc/remoteproc-core.yaml#"
> > +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
> > +
> > +title: Binding for the remoteproc core applicable to all remote processors
> > +
> > +maintainers:
> > +  - Bjorn Andersson <bjorn.andersson@...aro.org>
> > +  - Mathieu Poirier <mathieu.poirier@...aro.org>
> > +
> > +description:
> > +  This document defines the binding recognised by the remoteproc core that can
> > +  be used by any remote processor in the subsystem.
> > +
> > +properties:
> > +  autonomous-on-core-reboot:
> > +    $ref: /schemas/types.yaml#/definitions/flag
> > +    description:
> > +      Used in two situations, i.e when a user space application releases the
> > +      handle it has on the remote processor's character driver interface and
> > +      when a remote processor's platform driver is being removed.  If defined,
> > +      this flag instructs the remoteproc core to detach the remote processor
> > +      rather than turning it off.
> 
> Userspace? character driver? platform driver? remoteproc core? Please 
> explain this without OS specific terms.

The remoteproc state machine is gaining in complexity and having technical terms
in the binding's description helps understand when and how it should be used.  I
could make it more generic but that will lead to confusion and abuse.  Should I
make it "rproc,autonomous-on-core-reboot" ?

> 
> Seems to me this would be implied by functionality the remote proc 
> provides.

Exactly - this binding is used by the remoteproc core itself.  It is specified
in the remote processor DT nodes but the individual platform drivers don't do
anything with it - the core takes care of enacting the desired behavior on their
behalf.  Otherwise each platform driver would end up adding the same code, which
nobody wants to see happening.

How do you want me to proceed?

Thanks,
Mathieu

> 
> Rob