From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 63A2ACA5FA2 for ; Mon, 28 Sep 2026 16:37:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=iYA0hFIaMdYn488gGkJqtLh/o+HH8Ayao7MCR8wMWY0=; b=DJ1nZMLyT20rYl6Gr2n10YGG9E XkB1HnGDUXXosgV9PlV7plxQV+v1c2Hox2jE6aDeaPK2KnaczjN47ZpdtBbUE/NnrYIe0o/3tMSCX QVw9U/dO0qE/HoLiWXvaDm+Wdyj+oTl/K7TwLj/PPLQPIJsPWPO1tN4yjXLF+2igc+SNKp232pj5M jU3ZvPGD4zXd+OqKpD+z1ApNFF7cnAc+DtSi4s1my3eDmw60Agsk6bc8H82NkHLCO1INm0/J1OfwU Zj6xZVVn80bnRGPlQ10/ors5jC7y1zU9+rb0WLTmfSXwU49/twquFKpPQYxqgxOU6KYlIMltNDP/c oSgdS0OQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBELu-000000013BF-3KLL; Mon, 28 Sep 2026 16:37:18 +0000 Received: from perceval.ideasonboard.com ([213.167.242.64]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBELs-000000013AO-13yn; Mon, 28 Sep 2026 16:37:17 +0000 Received: from killaraus.ideasonboard.com (2001-14ba-70f3-e800--a06.rev.dnainternet.fi [IPv6:2001:14ba:70f3:e800::a06]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id D2BE68FD; Mon, 28 Sep 2026 18:35:22 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1790613323; bh=79ekLGQx1Tor6z02KqQn9lGJBkxxAMsnhhsc0gv/Pv4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tgwwdITKp4bfEl3NckTRce+gdM4AqUQST43w9pHEv3HmzcSUOqUmik84htz5qPg3X OcLpOr9Mikj4IUIaukMWgueo2gjofH/ExaxDKh1qFqsWzuUQvNYFgZg4MLBuMKQJqT zLI18YDW8IyTiyPLslMQtK6pLIx4CdsGLPz0oBLc= Date: Mon, 28 Sep 2026 19:37:11 +0300 From: Laurent Pinchart To: Maxime Ripard Cc: Neil Armstrong , Jessica Zhang , David Airlie , Simona Vetter , Maarten Lankhorst , Thomas Zimmermann , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Florian Fainelli , Broadcom internal kernel review list , Andrzej Hajda , Robert Foss , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Albert Esteve , Dave Stevenson , Javier Martinez Canillas , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, llvm@lists.linux.dev, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Benjamin Tissoires Subject: Re: [PATCH 0/6] drm/bridge: Add a BPF-based MIPI-DSI panel driver Message-ID: <20260928163711.GA210522@killaraus.ideasonboard.com> References: <20260928-drm-mipi-dsi-panel-ebpf-v1-0-5244926aace4@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260928-drm-mipi-dsi-panel-ebpf-v1-0-5244926aace4@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260928_093716_446882_9AC09EB0 X-CRM114-Status: GOOD ( 35.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 > --- > 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