linux-kernel - Re: [PATCH v4 1/7] dt-bindings: Add panel-timing subnode to simple-panel

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Date:   Fri, 29 Mar 2019 09:14:43 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Sean Paul <seanpaul@...omium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Enric Balletbò <enric.balletbo@...labora.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Eric Anholt <eric@...olt.net>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        Stéphane Marchesin <marcheu@...omium.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v4 1/7] dt-bindings: Add panel-timing subnode to simple-panel

Hi,

On Fri, Mar 29, 2019 at 9:13 AM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Thu, Mar 28, 2019 at 6:50 PM Doug Anderson <dianders@...omium.org> wrote:
> >
> > Hi,
> >
> >
> > On Thu, Mar 28, 2019 at 1:27 PM Ezequiel Garcia <ezequiel@...labora.com> wrote:
> > >
> > > On Thu, 2019-03-28 at 10:17 -0700, Douglas Anderson wrote:
> > > > From: Sean Paul <seanpaul@...omium.org>
> > > >
> > > > This patch adds a new subnode to simple-panel allowing us to override
> > > > the typical timing expressed in the panel's display_timing.
> > > >
> > > > Changes in v2:
> > > >  - Split out the binding into a new patch (Rob)
> > > >  - display-timings is a new section (Rob)
> > > >  - Use the full display-timings subnode instead of picking the timing
> > > >    out (Rob/Thierry)
> > > > Changes in v3:
> > > >  - Go back to using the timing subnode directly, but rename to
> > > >    panel-timing (Rob)
> > > > Changes in v4:
> > > >  - Simplify desc. for when override should be used (Thierry/Laurent)
> > > >  - Removed Rob H review since it's been a year and wording changed
> > > >
> > > > Cc: Doug Anderson <dianders@...omium.org>
> > > > Cc: Eric Anholt <eric@...olt.net>
> > > > Cc: Heiko Stuebner <heiko@...ech.de>
> > > > Cc: Jeffy Chen <jeffy.chen@...k-chips.com>
> > > > Cc: Rob Herring <robh+dt@...nel.org>
> > > > Cc: Stéphane Marchesin <marcheu@...omium.org>
> > > > Cc: Thierry Reding <thierry.reding@...il.com>
> > > > Cc: devicetree@...r.kernel.org
> > > > Cc: dri-devel@...ts.freedesktop.org
> > > > Cc: linux-rockchip@...ts.infradead.org
> > > > Signed-off-by: Sean Paul <seanpaul@...omium.org>
> > > > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > > > ---
> > > >
> > > >  .../bindings/display/panel/simple-panel.txt   | 24 +++++++++++++++++++
> > > >  1 file changed, 24 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/panel/simple-panel.txt b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> > > > index b2b872c710f2..6157f86ddce4 100644
> > > > --- a/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> > > > +++ b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> > > > @@ -15,6 +15,18 @@ Optional properties:
> > > >    (hot plug detect) signal, but the signal isn't hooked up so we should
> > > >    hardcode the max delay from the panel spec when powering up the panel.
> > > >
> > > > +panel-timing subnode
> > > > +--------------------
> > > > +
> > > > +This optional subnode is for devices which require a mode differing
> > > > +from the panel's "typical" display timing.  The panel timings provided
> > > > +here will be ignored if they are found to be outside of allowable
> > > > +ranges for the given panel.
> > > > +
> > >
> > > Is it OK to put this comment about how the implementation
> > > will behave when values are out of range, given this is just a binding
> > > spec?
> > >
> > > Perhaps -if needed- this sentence can be rephrased to state that,
> > > e.g. the OS may not be able to apply these values, if the controller
> > > or device is unable to?
> >
> > I will defer to Rob H. on this one, but I'm happy to simply remove the
> > last sentence.  I was trying to add a more OS-agnostic version of the
> > bullet points from V3 but agree that we could just remove this from
> > the bindings completely.
>
> Following my opinion that it's not the kernel's job to validate
> bindings, I would say it's fine for the OS to blindly apply them if it
> chooses.
>
> Plus with schema, you can provide the ranges of values and validate
> DTs up front (unless you want to validate some result of math
> operations).

OK, I'll remove the sentence and repost sometime early next week.  Thanks!

-Doug