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From:   "dbasehore ." <dbasehore@chromium.org>
Date:   Fri, 14 Jun 2019 17:43:09 -0700
Message-ID: <CAGAzgsqgbr5rWpyWB1H_66=kxBRb7kw4wE7h34TJfE7eJ1mSQQ@mail.gmail.com>
Subject: Re: [PATCH 1/5] drm/panel: Add helper for reading DT rotation
To:     Sam Ravnborg <sam@ravnborg.org>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Sean Paul <sean@poorly.run>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        CK Hu <ck.hu@mediatek.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        devicetree@vger.kernel.org,
        Intel Graphics <intel-gfx@lists.freedesktop.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>
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On Wed, Jun 12, 2019 at 2:18 PM Sam Ravnborg <sam@ravnborg.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@chromium.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
> The comment says "enum" but the type used is an int.
> Why not use enum drm_panel_orientation?
>

The binding is just an int value, but I can change it to the enum.

> > + *
> > + * 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.
> > + */
> Initially I read -EEROOR as a specific error code.
> But I gues the semantic is to say that a negative error code is returned
> if something was wrong.
> As we do not use the "-EERROR" syntax anywhere else in drm, please
> reword like we do in other places.
>
>
> Also - it is worth to mention that the rotation returned is
> DRM_MODE_PANEL_ORIENTATION_UNKNOWN if the property is not specified.
> I wonder if this is correct, as no property could also been
> interpretated as DRM_MODE_PANEL_ORIENTATION_NORMAL.
> And in most cases the roation property is optional, so one could
> assume that no property equals 0 degree.
>
>
>         Sam
>
> > +int of_drm_get_panel_orientation(const struct device_node *np, int *orientation)
> > +{
> > +     int rotation, ret;
> > +
> > +     ret = of_property_read_u32(np, "rotation", &rotation);
> > +     if (ret == -EINVAL) {
> > +             /* Don't return an error if there's no rotation property. */
> > +             *orientation = DRM_MODE_PANEL_ORIENTATION_UNKNOWN;
> > +             return 0;
> > +     }
> > +
> > +     if (ret < 0)
> > +             return ret;
> > +
> > +     if (rotation == 0)
> > +             *orientation = DRM_MODE_PANEL_ORIENTATION_NORMAL;
> > +     else if (rotation == 90)
> > +             *orientation = DRM_MODE_PANEL_ORIENTATION_RIGHT_UP;
> > +     else if (rotation == 180)
> > +             *orientation = DRM_MODE_PANEL_ORIENTATION_BOTTOM_UP;
> > +     else if (rotation == 270)
> > +             *orientation = DRM_MODE_PANEL_ORIENTATION_LEFT_UP;
> > +     else
> > +             return -EINVAL;
> > +
> > +     return 0;
> > +}
> > +EXPORT_SYMBOL(of_drm_get_panel_orientation);
> >  #endif
> >
> >  MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
> > diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> > index 8c738c0e6e9f..13631b2efbaa 100644
> > --- a/include/drm/drm_panel.h
> > +++ b/include/drm/drm_panel.h
> > @@ -197,11 +197,18 @@ int drm_panel_detach(struct drm_panel *panel);
> >
> >  #if defined(CONFIG_OF) && defined(CONFIG_DRM_PANEL)
> >  struct drm_panel *of_drm_find_panel(const struct device_node *np);
> > +int of_drm_get_panel_orientation(const struct device_node *np,
> > +                              int *orientation);
> >  #else
> >  static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
> >  {
> >       return ERR_PTR(-ENODEV);
> >  }
> > +int of_drm_get_panel_orientation(const struct device_node *np,
> > +                              int *orientation)
> > +{
> > +     return -ENODEV;
> > +}
> >  #endif
> >
> >  #endif
> > --
> > 2.22.0.rc2.383.gf4fbbf30c2-goog