On Friday, August 16, 2024 8:52:32 AM EDT Jocelyn Falempe wrote: > drm_log is a simple logger that uses the drm_client API to print the kmsg boot log on the screen. > This is not a full replacement to fbcon, as it will only print the kmsg. > It will never handle user input, or a terminal because this is better done in userspace. > > If you're curious on how it looks like, I've put a small demo here: > https://people.redhat.com/jfalempe/drm_log/drm_log_draft_boot_v2.mp4 > > Design decisions: > * It uses the drm_client API, so it should work on all drm drivers from the start. > * It doesn't scroll the message, that way it doesn't need to redraw the whole screen for each new message. > It also means it doesn't have to keep drawn messages in memory, to redraw them when scrolling. > * It uses a circular buffer so the console->write() callback is very quick, and will never stall. > * Drawing is done asynchronously using a workqueue. > * drm_log can only be built-in (and drm must be built-in too). > The reason is that, if you build it as a module, then a userspace application will be more appropriate than this module. > * When nbcon will be ready, I will use it. It should simplify this a lot, but I prefer not to depend on it yet. > > The first patch is not for review/merge, it's a squash of my pending drm_panic series: > https://patchwork.freedesktop.org/series/135944/ > > The second patch, moves the drawing function from drm_panic.c, to drm_draw.c, so they can be re-used by drm_log. > The next patches are the actual drm_log implementation. > > v2: > * Use vmap_local() api, with that change, I've tested it successfully on simpledrm, virtio-gpu, amdgpu, and nouveau. > * Stop drawing when the drm_master is taken. This avoid wasting CPU cycle if the buffer is not visible. > * Use deferred probe. Only do the probe the first time there is a log to draw. With this, if you boot with quiet, drm_log won't do any modeset. > * Add color support for the timestamp prefix, like what dmesg does. > * Add build dependency on disabling the fbdev emulation, as they are both drm_client, and there is no way to choose which one gets the focus. > > Thanks and best regards, > > I tested it, and it seems pretty cool. And fast, it seems to keep up when I echo 100,000 lines to /dev/kmsg with seq
