linux-kernel - Preferring cursor plane over overlay plane

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Message-ID: <5edad360-d05d-1bb8-c1f2-925138784fef@iki.fi>
Date:   Mon, 26 Mar 2018 14:14:00 +0000
From:   Joonas Kylmälä <joonas.kylmala@....fi>
To:     dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>, airlied@...ux.ie,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jernej Škrabec <jernej.skrabec@...l.net>
Cc:     linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Preferring cursor plane over overlay plane

Hi DRM subsystem developers,

I ran into this patch where overlay plane was switched to cursor plane
because there was no proper cursor plane available on the display
hardware: <https://lkml.org/lkml/2018/3/17/120>. Can we discuss whether
to have a policy of using a normal plane for cursor plane in case a
dedicated HW cursor plane is missing?

Daniel Vetter suggests that it might be fine to use normal plane for
cursor plane because how to use the plane would be only "a hint to
userspace" (see the email linked).

My motivation for having this discussion is that the newer Allwinner
SoCs don't have dedicated HW cursor plane and the sun4i DRM driver
currently uses the extra planes as overlay planes which makes moving the
cursor on Xfce4 DE a terrible experience. To have better cursor moving
experience one overlay plane would need to be sacrificed.

Also, I probably missed some recipients for this email so please forward
it to the recipients you think might be interested about this.

Best regards,
Joonas