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

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Message-ID: <d328299b-40c2-4e63-a3b9-c83feb1ca168@redhat.com>
Date: Mon, 7 Oct 2024 09:27:28 +0200
From: Jocelyn Falempe <jfalempe@...hat.com>
To: Caleb Connolly <caleb.connolly@...aro.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 John Ogness <john.ogness@...utronix.de>,
 Javier Martinez Canillas <javierm@...hat.com>,
 "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
 bluescreen_avenger@...izon.net, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] drm/log: Introduce a new boot logger to draw the
 kmsg on the screen

On 05/10/2024 00:40, Caleb Connolly wrote:
> 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

Thanks, it's a really nice demo!
For high-resolution screen, I will add integer scaling soon, so that 
should be a bit easier to read, without requiring huge fonts.

-- 

Jocelyn


> 
> Tested-by: Caleb Connolly <caleb.connolly@...aro.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
>