[PATCH v3 0/4] drm/log: Introduce a new boot logger to draw the kmsg on the screen

[Caleb Connolly]

Hi Jocelyn,

On 10/09/2024 08:56, 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.


I tried this out on the OnePlus 6 (Qualcomm SDM845/freedreno) and it 
looks great :D

Here's a demo for kicks:

https://people.linaro.org/~caleb.connolly/drm_log_oneplus6.mp4

Tested-by: Caleb Connolly <caleb.connolly at linaro.org> # freedreno/dsi

Kind regards,
> 
> 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.
>    * 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.
>    * It uses the new non-blocking console API, so it should work well with PREEMPT_RT
>   
> 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.
> 
> v3:
>   * Remove the work thread and circular buffer, and use the new write_thread() console API.
>   * Register a console for each drm driver.
> 
> Thanks and best regards,
> 
> Jocelyn Falempe (4):
>    drm/panic: Move drawing functions to drm_draw
>    drm/log: Introduce a new boot logger to draw the kmsg on the screen
>    drm/log: Do not draw if drm_master is taken
>    drm/log: Color the timestamp, to improve readability
> 
>   drivers/gpu/drm/Kconfig     |  19 ++
>   drivers/gpu/drm/Makefile    |   3 +
>   drivers/gpu/drm/drm_draw.c  | 216 ++++++++++++++++++++
>   drivers/gpu/drm/drm_draw.h  |  56 ++++++
>   drivers/gpu/drm/drm_drv.c   |   2 +
>   drivers/gpu/drm/drm_log.c   | 391 ++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/drm_log.h   |  11 +
>   drivers/gpu/drm/drm_panic.c | 247 +++--------------------
>   8 files changed, 721 insertions(+), 224 deletions(-)
>   create mode 100644 drivers/gpu/drm/drm_draw.c
>   create mode 100644 drivers/gpu/drm/drm_draw.h
>   create mode 100644 drivers/gpu/drm/drm_log.c
>   create mode 100644 drivers/gpu/drm/drm_log.h
> 
> 
> base-commit: 9aaeb87ce1e966169a57f53a02ba05b30880ffb8

-- 
// Caleb (they/them)