From: Thomas Zimmermann <tzimmermann@suse.de>
To: Maxime Ripard <mripard@kernel.org>, Francesco Valla <francesco@valla.it>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
Jonathan Corbet <corbet@lwn.net>,
Jocelyn Falempe <jfalempe@redhat.com>,
Javier Martinez Canillas <javierm@redhat.com>,
Sam Ravnborg <sam@ravnborg.org>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-doc@vger.kernel.org, linux-embedded@vger.kernel.org
Subject: Re: [PATCH RFC 0/3] Add splash DRM client
Date: Mon, 27 Oct 2025 13:35:31 +0100 [thread overview]
Message-ID: <3edea192-6a3f-44f5-b570-7033776e2ce4@suse.de> (raw)
In-Reply-To: <yq4btdc5qqukuqps7y53dratmu64ghyifgprlndnk5rbgml4of@rvca75sncvsm>
Hi Francenso, Maxime,
Am 27.10.25 um 11:09 schrieb Maxime Ripard:
> Hi,
>
> On Mon, Oct 27, 2025 at 12:03:00AM +0100, Francesco Valla wrote:
>> this patchset adds a new DRM client offering splash functionalities,
>> able to draw to screen:
>>
>> - a colored background;
> So, I like that part, and we were recently discussing about this.
The panic screen has configurable foreground/background colors. Maybe we
can harmonize these settings.
>
>> - a single-line text message, which can be set through sysfs or
>> directly from the kernel command line;
Put it into the kernel config.
>> - a very simple progress bar, which can be driven through sysfs;
Once you have options to control these settings from user space, you
should do it in user space entirely. As Maxime suggested, please improve
plymouth for anything with animation.
>> - a static image (optional).
Board vendors often provide an image, see /sys/firmware/acpi/bgrt/. This
is a candidate for display, or the penguin or a custom image. Please
make it configurable by Kconfig. Again, if you need policy and
heuristics for deciding what to display, you better do this in user space.
> But there's no reason to have all that in the kernel, and we already
> have userspace components to do so (plymouth being the main "mainstream"
> one).
>
>> Once compiled inside the kernel, the client can be enabled through the
>> command line specifying the drm_client_lib.active=splash parameter.
>>
>> == Motivation ==
>>
>> The motivation behind this work is to offer to embedded system
>> developers a new path for a simple activation of the display(s)
>> connected to their system, with the following usecases:
>>
>> - bootsplash - possibly displaying even before init;
>> - early activation of the display pipeline, in particular whenever one
>> component of the pipeline (e.g.: a panel) takes a non-negligible
>> time to initialize;
>> - recovery systems, where the splash client can offer a simple feedback
>> for unattended recovery tasks;
>> - update systems, where the splash client can offer a simple feedback
>> for unattended update tasks.
> If plymouth cannot be used by embedded systems for some reason, then you
> should work on a plymouth alternative.
Agreed. With an updater running in user space, that process should also
manage the display update. No need for this in the kernel.
>
>> While the first seems the most obvious one, it was the second that acted
>> as the driver, as in the past I had to implement a ugly workaround using
>> a systemd generator to kickstart the initialization of a display and
>> shave ~400ms of boot time.
>>
>> The last 2 usecase, instead, are the reason I dropped the "boot" part
>> from bootsplash.
>>
>> == Implementation details ==
>>
>> The design is quite simple, with a kernel thread doing the heavylifting
>> for the rendering part and some locking to protect interactions with it.
>>
>> The splash image is loaded using the firmware framework, with the client
>> expecting to find a binary dump having the right dimensions (width and
>> height) and FOURCC format for each modeset. Given a 1920x1080 RGB888
>> modeset, the client will for example search for a firmware named:
>>
>> drm_splash_1920x1080_RG24.raw
>>
>> If the firmware cannot be loaded directly, the NOUEVENT sysfs fallback
>> mechanism is used to let userspace load the appropriate image.
>>
>> == Testing ==
>>
>> Testing was done on qemu (both with vkms and bochs drivers), on a HDMI
>> display connected to a Beagleplay and on a ILI9341 SPI display connected
>> to a i.MX93 FRDM board. All these platforms revealed different
>> weaknesses that were hopefully removed.
>>
>> == Open points / issues ==
>>
>> The reason for this being an RFC is that there are several open points:
>>
>> - Support for tiled connectors should be there, but has not been
>> tested. Any idea on how to test it?
> Did you mean tiled formats?
>
>> - I'm not entirely convinced that using the firmware framework to load
>> the images is the right path. The idea behind it was to re-use the
>> compressed firmware support, but then I discovered it is not there
>> for built-in firmware.
> Yeah, firmware loading for this has a few issues (being tedious to setup
> for when built-in being one). I think just going the fbdev penguin road
> is a better choice: you provide the path, and it's embedded in the
> kernel directly.
>
>> - Again on the firmware loading: CONFIG_LOADPIN would interfere with
>> sysfs loading.
>> - And again: FW_ACTION_NOUEVENT only has one user inside the kernel,
>> leading me to think it is de-facto deprecated. And still, uevents
>> for firmware loading seem frowned upon these days...
>> - Generating binary dumps for... basically any format is not so
>> straightforward. I crafted a Python tool with AI help which seems
>> to work quite well, but I honestly did not yet understood which is
>> the policy for AI-generated code inside the kernel, so it is not
>> included in this patch set. All client code is genuine, though.
> BMP is simple enough to support so we should probably use that instead
> of a custom format.
file /sys/firmware/acpi/bgrt/image
/sys/firmware/acpi/bgrt/image: PC bitmap, Windows 3.x format, 768 x 256
x 24, image size 589824, cbSize 589878, bits offset 54
That should probably be the format for now unless your firmware uses
something else natively. Code for reading a BMP file can be found in the
efifb driver. [1]
[1]
https://elixir.bootlin.com/linux/v6.17.5/source/drivers/video/fbdev/efifb.c#L24
Apart from the criticism for complexity, I do like the idea of having a
splash screen.
Best regards
Thomas
>
> Maxime
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
next prev parent reply other threads:[~2025-10-27 12:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-26 23:03 [PATCH RFC 0/3] Add splash DRM client Francesco Valla
2025-10-26 23:03 ` [PATCH RFC 1/3] drm: client: add splash client Francesco Valla
2025-10-26 23:03 ` [PATCH RFC 2/3] MAINTAINERS: add entry for DRM " Francesco Valla
2025-10-26 23:03 ` [PATCH RFC 3/3] drm: docs: remove bootsplash from TODO Francesco Valla
2025-10-27 10:09 ` [PATCH RFC 0/3] Add splash DRM client Maxime Ripard
2025-10-27 12:35 ` Thomas Zimmermann [this message]
2025-10-27 16:01 ` Mario Limonciello
2025-10-27 16:28 ` Maxime Ripard
2025-10-27 16:31 ` Mario Limonciello
2025-10-27 17:19 ` Maxime Ripard
2025-10-28 8:09 ` Francesco Valla
2025-10-28 13:39 ` Mario Limonciello
2025-10-29 8:36 ` Maxime Ripard
2025-10-28 8:03 ` Francesco Valla
2025-10-28 7:58 ` Francesco Valla
2025-10-29 8:34 ` Maxime Ripard
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