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 <[email protected]> > --- > 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
