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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 ADD08CA5FA7 for ; Tue, 29 Sep 2026 09:33:10 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 08B8710E9C0; Tue, 29 Sep 2026 09:33:10 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="g1fEQqx6"; dkim-atps=neutral Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by gabe.freedesktop.org (Postfix) with ESMTPS id 95CCD10E9C0 for ; Tue, 29 Sep 2026 09:33:07 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id BE7E560008; Tue, 29 Sep 2026 09:33:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3EC61F000FF; Tue, 29 Sep 2026 09:33:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790674386; bh=7my33tHkcnAh5NzGYvJklT1PtJEphsrY3nRhIAu2WEM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=g1fEQqx6q9GJjmXIa4fL4LunigoQ8sYi2oCnV0YG6aD4gqsX6MV47f2rOQBdyupOR ZDxf/muo0fXP9Ml6XxfjgNPPwvXz2a3H/ma4tOKFvuPcDQp8QRg5hb5NjKMDWi7qHN lJ5bX1GB8/u+X5Kk26FqdWLRuotq6M/89CVYEYjsPQ/VvOgAd6e8A7qefsNexpVjbO pv29vxAcIhf798lWkQL0VXtsEuguV0bopYfBjxfp9H9xT7akHCUxNpl3QDa6NuaIPU masy6oFHXPWXl/kzWZSoL3BEHwMMMMrWOs9IwXJaDxiz865Aa/NxzzudsvYWCX5F3t SZ/A6FUd2Y6uQ== Date: Tue, 29 Sep 2026 11:32:57 +0200 From: Benjamin Tissoires To: Jani Nikula Cc: Maxime Ripard , 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 , Laurent Pinchart , 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 Subject: Re: [PATCH 0/6] drm/bridge: Add a BPF-based MIPI-DSI panel driver Message-ID: References: <20260928-drm-mipi-dsi-panel-ebpf-v1-0-5244926aace4@kernel.org> <054ef52478fc93fc213a9dae23ea77f73094aaf2@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <054ef52478fc93fc213a9dae23ea77f73094aaf2@intel.com> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Sep 29 2026, Jani Nikula wrote: > On Mon, 28 Sep 2026, Maxime Ripard wrote: > > 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. > > I'd think for most panels it would suffice to have a declarative > language describing what to do at what points in time. For example, at > poweron, enable this GPIO, wait a little, write this set of DSI > commands, etc. You rarely need actual programming, or even ability to > read-modify-write something. TBH, that's exactly how Maxime presented the idea to me before submitting this. > > It could be, say, YAML converted to some binary representation. Maybe > that could be in the DT, or maybe you could override it with the > firmware loader. And obviously any vendor "blob" could be trivially > converted back to YAML and upstreamed. Ouch. This immediately raises the "let's implement a parser in the kernel" flag, or "let's create a new langage". That's exactly what BPF is: ou have a source file (in C, rust, whatever) that is converted to a binary blob that the kernel already knows how to use and that is safe to load, and we can easily go back to the sources. > > Where that falls short, you could always have a dedicated driver, or > extend the declarative stuff. See Maxime's answers: yes, falling back to dedicated driver is still encouraged. > > Now, the question is, how much more BPF solves over that, without > requiring a dedicated driver, and is the added complexity worth it? You'd still need a dedicated driver for your new blob parser, with far fewer people who had had a look at it than BPF who has been working on for several years. The integration of BPF and the kernel is honestly transparent nowaday: calling a struct_ops BPF function is just a function call away, and from the bpf calling anything in the kernel is also just a call away. > > FWIW, on the Intel platforms that support DSI, all of the > initialization, poweron/poweroff, backlight on/off etc. sequences like > that are stored in the BIOS, defined by the OEM. A plethora of DSI > panels, one driver. Don't look at it for examples how to implement it, > but I think the basic idea is workable. Isn't that what Maxime wants to have? One driver for a plethora of DSI panels, with the same ability the BIOS has to also do function calls to set things up? Cheers, Benjamin