On Mon, Mar 26, 2018 at 11:01:53PM +0800, Chen-Yu Tsai wrote:
On Mon, Mar 26, 2018 at 10:45 PM, Maxime Ripard maxime.ripard@bootlin.com wrote:
On Mon, Mar 26, 2018 at 10:22:45PM +0800, Chen-Yu Tsai wrote:
On Mon, Mar 26, 2018 at 10:14 PM, Joonas Kylmälä joonas.kylmala@iki.fi wrote:
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.
If you look at the development history, we've never supported cursor planes.
X can use an overlay to put the cursor though.
At the beginning we supported one main plane and one overlay plane. That was it. The Display Engine 1.0 does have support for an extra hardware cursor, but we haven't done the work to support it yet. I don't know about the Display Engine 2.0 though.
An issue with supporting the hardware cursor we have is that as far as I understood, the cursor plane in DRM has the assumption that it would be an ARGB format. In the first display engine, the format is actually an 8-bit palette with 1 bit of alpha iirc.
Looks like it's 32x32 pixels with an 8-bit (max) palette, with full RGBA for the colors in the palette. I don't see the 1 bit alpha you mentioned. Looks like this needs some extra work for building the palette and copying the cursor image.
Indeed, you're right. I'm still not sure how it could be turned into something useful though.
Maxime