Re: [PATCH 0/6] drm/bridge: Add a BPF-based MIPI-DSI panel driver

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Maxime,

On Mon, Sep 28, 2026 at 06:22:00PM +0200, Maxime Ripard wrote:
> Hi,
> 
> Panels in general, and MIPI-DSI panels in particular, are pretty
> difficult to support and require pretty much a panel driver for each
> panel produced. Most of them are pretty simple, and require an opaque
> initialization sequence that is usually poorly documented.
> 
> This creates a tension between OEMs and distros because OEMs will
> typically get a new panel to react to a sourcing issue during
> production, and thus need some swift turnaround between getting their
> new panel and it being operational in the OS. Distributions on the other
> hand can take years to ship a kernel with that new panel driver.
> 
> To solve this, I followed the example of HID-BPF and wrote a panel
> driver that will rely on BPF programs to perform the panel
> initialization. That way, we can ship the programs separately from the
> kernel, and with a different lifecycle. If this driver is accepted, the
> plan is to have a userspace component started by udev to identify and
> load the right BPF program for the panels found on the device.

Interesting idea.

How would that work for devices that want early display support ? In
particular, how does it interact with your recent work on "fastboot"
support (with the kernel drivers taking over a running display
configured by the boot loader) ?

I'm also wondering about the incentives for vendors to upstream the
code. How will we avoid having a proliferation of out-of-tree drivers ?

> This driver is fully functional and works with both 5" and 7" Touch
> Display 2 panels for the RaspberryPi. However, it breaks away from the
> typical panel driver in multiple ways:
> 
> - BPF programs can only be loaded by userspace. This leaves us with two
>   choices: 
> 
>   * We prevent the driver from loading until the script itself is
>     loaded. This has the side effect of preventing any other output to
>     be used until the initramfs is ran at the earliest, and possibly
>     ever if the loader isn't installed for example.
> 
>   * Or we probe the driver all the time, but only report it as connected
>     once a program has been registered. This is somewhat unconventional,
>     but allows the other outputs to be functional, *and* allows the user
>     to force the output if their panel doesn't require any
>     initialization or during debugging. I chose this solution.
> 
> - It's not a panel driver, but a bridge one, which is also pretty
>   unconventional. This is required because panel drivers don't have
>   access to a detect callback that is required for the above, but I also
>   think that the recent work from Luca blurs the line from panels and
>   bridges and we'll end up going that road anyway.
> 
> Let me know what you think,
> Maxime
> 
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
> Maxime Ripard (6):
>       dt-bindings: display: Add panel-mipi-dsi-bpf generic panel binding
>       drm/panel: Add generic MIPI-DSI panel driver with BPF init sequences
>       drm/panel: dsi-bpf: Add BPF program build infrastructure and helper header
>       drm/panel: dsi-bpf: Add Raspberry Pi 7-inch panel BPF program
>       drm/panel: dsi-bpf: Add Raspberry Pi 5-inch panel BPF program
>       [DO NOT MERGE] arm64: dts: broadcom: Add Raspberry Pi ILI9881C DSI panel overlays
> 
>  .../bindings/display/panel/panel-mipi-dsi-bpf.yaml | 184 +++++++++
>  arch/arm64/boot/dts/broadcom/Makefile              |   8 +
>  .../bcm2711-rpi-4-b-dsi-ili9881-5inch.dtso         |  22 +
>  .../bcm2711-rpi-4-b-dsi-ili9881-7inch.dtso         |  22 +
>  .../dts/broadcom/bcm2711-rpi-4-b-dsi-ili9881.dtsi  |  65 +++
>  drivers/gpu/drm/panel/Kconfig                      |   3 +
>  drivers/gpu/drm/panel/Makefile                     |   1 +
>  drivers/gpu/drm/panel/bpf/Kconfig                  |  28 ++
>  drivers/gpu/drm/panel/bpf/Makefile                 |  10 +
>  .../gpu/drm/panel/bpf/panel-bpf-mipi-dsi-core.c    | 452 +++++++++++++++++++++
>  .../gpu/drm/panel/bpf/panel-bpf-mipi-dsi-kfuncs.c  | 278 +++++++++++++
>  drivers/gpu/drm/panel/bpf/panel-bpf-mipi-dsi-ops.c | 242 +++++++++++
>  .../gpu/drm/panel/bpf/panel-bpf-mipi-dsi-trace.c   |   4 +
>  .../gpu/drm/panel/bpf/panel-bpf-mipi-dsi-trace.h   | 246 +++++++++++
>  drivers/gpu/drm/panel/bpf/panel-bpf-mipi-dsi.h     | 264 ++++++++++++
>  drivers/gpu/drm/panel/bpf/progs/Makefile           |  93 +++++
>  .../panel/bpf/progs/Raspberrypi__dsi-5inch.bpf.c   | 266 ++++++++++++
>  .../panel/bpf/progs/Raspberrypi__dsi-7inch.bpf.c   | 271 ++++++++++++
>  .../gpu/drm/panel/bpf/progs/panel-bpf-mipi-dsi.h   |  95 +++++
>  19 files changed, 2554 insertions(+)
> ---
> base-commit: 6e375de99d0c420169481fcd36064177ab55b09d
> change-id: 20260928-drm-mipi-dsi-panel-ebpf-d78b72a9c47f

-- 
Regards,

Laurent Pinchart