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

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Message-ID: <CAL_JsqKq1zM569nPLYNgj9WUHWO98nYYt6dBvHzLRMCKq5=T8g@mail.gmail.com>
Date:   Thu, 10 Dec 2020 17:10:36 -0600
From:   Rob Herring <robh@...nel.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "open list:REMOTE PROCESSOR (REMOTEPROC) SUBSYSTEM" 
        <linux-remoteproc@...r.kernel.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnaud POULIQUEN <arnaud.pouliquen@...com>
Subject: Re: [PATCH v3 01/15] dt-bindings: remoteproc: Add bindind to support
 autonomous processors

On Tue, Dec 1, 2020 at 5:43 PM Mathieu Poirier
<mathieu.poirier@...aro.org> wrote:
>
> 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.

Explaining in Linux specific terms will confuse any other OS user.

>  Should I
> make it "rproc,autonomous-on-core-reboot" ?

No, 'rproc' is not a vendor.

> >
> > 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.

The platform drivers just need to set a flag to enable some behavior
that the core code checks and handles. That should be 1 to a few lines
in the drivers. It's not really any different, just a question of
where the flag lives.

Rob