On 18/12/2024 12:00, Geert Uytterhoeven wrote:
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.
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.
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.
Best regards,
--
Jocelyn
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
