From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C9EFD37AA7A; Tue, 29 Sep 2026 09:33:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790674387; cv=none; b=l8l+/3uL4gjCebyTi68G8cKWxeuM76zfqU3AGXCwcvSO80M/vltiVz59g97TU1VYs/Ukp/vYv/YP1J+z7N3clTFM4JBfSRXl6aRIebGCjjZ52AFhN/GJF7TC/U05FmuX9bc2X2XqEIq0Mu1irZyYsExjupHeO0TAC6s3/KR5XoA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790674387; c=relaxed/simple; bh=egp61g4fx32yp6WAEsrcn+kHQU8ltab5JqPn7OiECDY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=oipCc0wtYj13YyQFiOvaOb4yiK1wMEdogM5HRNsBOWAy5/rgQz4X4x96ogHYuZ46OU9Nz0IAfH4YFM3S3U/LC4F4n34PKysj8Y/kk597co7jU6upql+oMEpxsJUSCehzCifQ5cyYBMgaKzL0vbNaX4nA5mznuw79zO0PJuPpuP8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g1fEQqx6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g1fEQqx6" 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <054ef52478fc93fc213a9dae23ea77f73094aaf2@intel.com> 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