Hi Petr, On Wed, Dec 18, 2024 at 3:18 PM Petr Mladek <pmladek@xxxxxxxx> wrote: > On Wed 2024-12-18 12:41:39, Jocelyn Falempe wrote: > > On 18/12/2024 12:00, Geert Uytterhoeven wrote: > > > 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. > > > > Yes, the fbcon console is tty0, which is hardcoded for historical reason. > > Some architectures use add_preferred_console() to enable specific consoles, > > I'm not sure it's allowed to use that from the drm_log_register() code. > > add_preferred_console() is used when the console should get enabled > intentionally. I would split the intentions into two categories: > > + requested by the end-user on the command line, see > __add_preferred_console(..., true) in console_setup() > > + enabled by default by a hardware definition (manufacture), see > add_preferred_console() in: > > + of_console_check(): generic solution via device tree > + acpi_parse_spcr(): generic solution via SPCR table > + *: hardcoded in few more HW-specific drivers > > add_preferred_console() causes the console will always get enabled > when it is successfully initialized. > > So, should the "drm_log" console get always enabled? Good question! > > I will still send a patch to add update the Kconfig help for drm_log, as > > this command line argument is required to have it working. > > I guess that the drm_log consoles should get enabled only when > requested by the user => documenting the command line parameter > is the right solution here. There are actually two ways to request it: 1. Through CONFIG_DRM_CLIENT_DEFAULT, at kernel configuration time, 2. Through drm_client_lib.active=log, at kernel boot or module load time. Currently both options need console=drm_log on top of that, which sounds like overkill? 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
