Hi Sebastian,
On Tue, Jan 12, 2021 at 05:24:54PM +0100, Sebastian Reichel wrote:
[dropped linux-next from Cc]
Hi,
On Tue, Jan 12, 2021 at 03:10:56PM +0200, Tomi Valkeinen wrote:
But why is it it we need omapfb at all when we have omapdrm?
I think there are two reasons omapfb has not been killed yet. One reason was missing support for manually updated DSI panels, which have been working since 1 or 2 kernel releases now. The other reason is some people using it in combination with an out-of-tree PowerVR kernel driver. There is currently work going on to use a more recent PowerVR driver based on omapdrm driven by Maemo Leste people.
omapfb also has a custom sysfs API, so applications that depend on it would not work anymore. I don't know if there are such applications, though.
Can we sunset all or some parts of omap support in video/? If not, what is missing to do so.
IDK the exact status of the PowerVR work and have not been using omapfb myself for years. I don't think there is a reason to rush this, so my suggestion is removing it in 3 steps giving people the chance to complain:
- Add 'depends on EXPERT' to 'FB_OMAP2' and add deprecation notice referencing omapdrm in help text in 5.12
- Add 'depends on BROKEN' in 5.13
- Drop drivers/video/fbdev/omap2 afterwards
I'd love to remove omapfb, but I also fear that there are still people using it. We can try the above sequence, but it's probably better to go slower, as people may not be using the latest kernels.
I thought about this again and I think the best option is to rename CONFIG_FB_OMAP2 to something like CONFIG_FB_OMAP2_DEPRECATED and update the help text. That way anyone with CONFIG_FB_OMAP2 in their .config will definitely notice the change when upgrading to a newer kernel, but can easily fix it temporarily. Help text could be
"This driver will be removed in 2022, please switch to omapdrm."
and no other intermediate steps are required that way :)
The plan looks good to me.
But while looking through CONFIG_FB_OMAP2 references I noticed there is also a V4L2 driver (CONFIG_VIDEO_OMAP2_VOUT), which seems to only work with omapfb. IIUIC that driver provides display overlays to V4L. I guess on omapdrm V4L can use DRM planes instead and no driver is needed (i.e. this driver could just go away with omapfb)?
One feature that the omapfb2 and the omap-vout drivers provide is rotation support with VRFB on OMAP3. I haven't moved to omapdrm on an old project for this reason. It should be possible to implement rotation support in omapdrm, but I'm not aware of any effort in that direction.