linux-kernel - Re: [PATCH v4 0/8] Add a panel API to return panel orientation

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Date:   Mon, 6 Jun 2022 21:28:40 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        Rob Clark <robdclark@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/8] Add a panel API to return panel orientation

Hi Hsin-Yi,
thanks for this nice series.

On Mon, Jun 06, 2022 at 11:24:23PM +0800, Hsin-Yi Wang wrote:
> Panels usually call drm_connector_set_panel_orientation(), which is
> later than drm/kms driver calling drm_dev_register(). This leads to a
> WARN()[1].
> 
> The orientation property is known earlier. For example, some panels
> parse the property through device tree during probe.
> 
> The series add a panel API drm_panel_get_orientation() for drm/kms
> drivers. The drivers can use the API to get panel's orientation, so they
> can call drm_connector_set_panel_orientation() before drm_dev_register().
> 
> Panel needs to implement .get_orientation callback to return the property.

The following comment appears in every panel driver:
+       /*
+        * drm drivers are expected to call drm_panel_get_orientation() to get
+        * panel's orientation then drm_connector_set_panel_orientation() to
+        * set the property before drm_dev_register(). Otherwise there will be
+        * a WARN_ON if orientation is set after drm is registered.
+        */

Please move it to the drm_panel c or h file, it is noise to add it to
all panel drivers.

	Sam