linux-kernel - Re: [PATCH 1/5] drm/panel: Add helper for reading DT rotation

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Date:   Thu, 13 Jun 2019 17:32:21 -0700
From:   "dbasehore ." <dbasehore@...omium.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH 1/5] drm/panel: Add helper for reading DT rotation

On Wed, Jun 12, 2019 at 2:20 PM Sam Ravnborg <sam@...nborg.org> wrote:
>
> Hi Derek.
>
> On Mon, Jun 10, 2019 at 09:03:46PM -0700, Derek Basehore wrote:
> > This adds a helper function for reading the rotation (panel
> > orientation) from the device tree.
> >
> > Signed-off-by: Derek Basehore <dbasehore@...omium.org>
> > ---
> >  drivers/gpu/drm/drm_panel.c | 41 +++++++++++++++++++++++++++++++++++++
> >  include/drm/drm_panel.h     |  7 +++++++
> >  2 files changed, 48 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> > index dbd5b873e8f2..3b689ce4a51a 100644
> > --- a/drivers/gpu/drm/drm_panel.c
> > +++ b/drivers/gpu/drm/drm_panel.c
> > @@ -172,6 +172,47 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
> >       return ERR_PTR(-EPROBE_DEFER);
> >  }
> >  EXPORT_SYMBOL(of_drm_find_panel);
> > +
> > +/**
> > + * of_drm_get_panel_orientation - look up the rotation of the panel using a
> > + * device tree node
> > + * @np: device tree node of the panel
> > + * @orientation: orientation enum to be filled in
> > + *
> > + * Looks up the rotation of a panel in the device tree. The rotation in the
> > + * device tree is counter clockwise.
> > + *
> > + * Return: 0 when a valid rotation value (0, 90, 180, or 270) is read or the
> > + * rotation property doesn't exist. -EERROR otherwise.
> > + */
> > +int of_drm_get_panel_orientation(const struct device_node *np, int *orientation)
> > +{
> > +     int rotation, ret;
> > +
> > +     ret = of_property_read_u32(np, "rotation", &rotation);
>
> I just noticed that everywhere this code talks about orientation,
> but the property that it reads are rotation.
> To my best understanding these are not the same.

This is because both were previously defined in the kernel. Rotation
was defined as a binding in the devicetree for panels (which is where
we wanted to put this property) and orientation already exists as a
DRM property.

If we want to change one, I would suggest the rotation binding since
it doesn't have any upstream users yet.

>
>         Sam