Hi Jocelyn, On Wed, Dec 18, 2024 at 11:14 AM Jocelyn Falempe <jfalempe@xxxxxxxxxx> wrote: > On 17/12/2024 15:54, Geert Uytterhoeven wrote: > > On Tue, Dec 17, 2024 at 3:46 PM Jocelyn Falempe <jfalempe@xxxxxxxxxx> wrote: > >> On 17/12/2024 15:19, Geert Uytterhoeven wrote: > >>> On Wed, Dec 4, 2024 at 6:41 PM Jocelyn Falempe <jfalempe@xxxxxxxxxx> 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 the new non-blocking console API, so it should work well with PREEMPT_RT > >>> > >>> I gave this a try on Koelsch (R-Car M2-W), using rcar-du. > >>> Unfortunately I don't see any kernel messages, and my monitor complains > >>> about no signal. Does this require special support from the driver? > >> > >> It doesn't require a special support from the driver. But as it is the > >> first drm client other than fbdev emulation, I'm not surprised it's > >> broken on some driver. > >> I know it works on virtio-gpu, nouveau, amdgpu, and even on a OnePlus 6 > >> (Qualcomm SDM845/freedreno), without requiring driver changes. > >> > >> Do you have a serial console on this device, to check if there is > >> something in kmsg? > > > > Nothing interesting to see. Compared to the fbdev client: > > > > rcar-du feb00000.display: [drm] Registered 2 planes with drm panic > > [drm] Initialized rcar-du 1.0.0 for feb00000.display on minor 0 > > rcar-du feb00000.display: [drm] Device feb00000.display probed > > -Console: switching to colour frame buffer device 240x67 > > -rcar-du feb00000.display: [drm] fb0: rcar-dudrmfb frame buffer device > > > > I did verify (by adding my own debug prints) that the code does > > get to the success case in drm_log_register(). > > Thanks! > > Maybe you need to add console=drm_log to your kernel command line, so > the kernel will actually use this console. Thanks, that does the trick! Note that I do not need to specify any console= kernel command line parameter for the fbdev console. With CONFIG_VT_CONSOLE=y CONFIG_DRM_CLIENT_DEFAULT_FBDEV=y I see all console messages on both the emulated fbdev console and on the serial console by default. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
