Re: [PATCH] fbdev: Remove udlfb driver

On Mon, 30 Nov 2020, Daniel Vetter wrote:

On Mon, Nov 30, 2020 at 01:39:17PM -0500, Mikulas Patocka wrote:

quoted

On Mon, 30 Nov 2020, Daniel Vetter wrote:

quoted

On Mon, Nov 30, 2020 at 09:31:15AM -0500, Mikulas Patocka wrote:

quoted

The framebuffer driver supports programs running full-screen directly on 
the framebuffer console, such as web browser "links -g", image viewer 
"fbi", postscript+pdf viewer "fbgs", ZX Spectrum emulator "fuse-sdl", 
movie player "mplayer -vo fbdev". The DRM driver doesn't run them.

Hm this should in general work on drm drivers. Without that it's clear the
switch-over isn't really ready yet.

I fixed it with this patch two years ago: 
https://lists.freedesktop.org/archives/dri-devel/2018-June/179023.html

But the patch never went through and the fb_defio feature was removed in 
the kernel 5.6 (commit d0c4fc5a4814e431c15272935c8dc973c18073aa).

The generic fbdev emulation still has a defio implementation. We could try
to make it more efficient maybe, but it should be all there. The module
option disappeared since you now should always get it by default.

Yes, it's there. I've tried to run links on the current DRM UDL driver and 
it displays correctly - except, that the page list gets sometimes 
corrupted and a crash happens.

quoted

Without fb_defio, the only other possibility how to update the screen is 
the ioctl DRM_IOCTL_MODE_DIRTYFB. But this ioctl requires master mode, so 
user programs like "links -g" can't issue it.

Now I'm confused, I thought you wanted to use fbdev /dev/fb* nodes? Those
should support defio. And if you want your applications to use drm
modesetting natively, they have to be drm master anyway. You can't use the
DIRTYFB ioctl to upload fbdev contents. So I'm a bit confused.
-Daniel

Yes. I was confused about it too. You can't use DRM ioctls on /dev/fb.

Mikulas