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[142.127.77.63]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67680ac3521sm764290d50.1.2026.09.30.07.01.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Sep 2026 07:01:56 -0700 (PDT) Message-ID: <6c581ae0-2480-47a2-b46e-97afadbc7c1f@linaro.org> Date: Wed, 30 Sep 2026 16:01:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Neil Armstrong Subject: Re: [PATCH 0/6] drm/bridge: Add a BPF-based MIPI-DSI panel driver To: Jani Nikula , Maxime Ripard , 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 Cc: 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, Benjamin Tissoires References: <20260928-drm-mipi-dsi-panel-ebpf-v1-0-5244926aace4@kernel.org> <054ef52478fc93fc213a9dae23ea77f73094aaf2@intel.com> Content-Language: en-US, fr Autocrypt: addr=neil.armstrong@linaro.org; keydata= xsBNBE1ZBs8BCAD78xVLsXPwV/2qQx2FaO/7mhWL0Qodw8UcQJnkrWmgTFRobtTWxuRx8WWP GTjuhvbleoQ5Cxjr+v+1ARGCH46MxFP5DwauzPekwJUD5QKZlaw/bURTLmS2id5wWi3lqVH4 BVF2WzvGyyeV1o4RTCYDnZ9VLLylJ9bneEaIs/7cjCEbipGGFlfIML3sfqnIvMAxIMZrvcl9 qPV2k+KQ7q+aXavU5W+yLNn7QtXUB530Zlk/d2ETgzQ5FLYYnUDAaRl+8JUTjc0CNOTpCeik 80TZcE6f8M76Xa6yU8VcNko94Ck7iB4vj70q76P/J7kt98hklrr85/3NU3oti3nrIHmHABEB AAHNKk5laWwgQXJtc3Ryb25nIDxuZWlsLmFybXN0cm9uZ0BsaW5hcm8ub3JnPsLAkQQTAQoA OwIbIwULCQgHAwUVCgkICwUWAgMBAAIeAQIXgBYhBInsPQWERiF0UPIoSBaat7Gkz/iuBQJk Q5wSAhkBAAoJEBaat7Gkz/iuyhMIANiD94qDtUTJRfEW6GwXmtKWwl/mvqQtaTtZID2dos04 YqBbshiJbejgVJjy+HODcNUIKBB3PSLaln4ltdsV73SBcwUNdzebfKspAQunCM22Mn6FBIxQ GizsMLcP/0FX4en9NaKGfK6ZdKK6kN1GR9YffMJd2P08EO8mHowmSRe/ExAODhAs9W7XXExw UNCY4pVJyRPpEhv373vvff60bHxc1k/FF9WaPscMt7hlkbFLUs85kHtQAmr8pV5Hy9ezsSRa GzJmiVclkPc2BY592IGBXRDQ38urXeM4nfhhvqA50b/nAEXc6FzqgXqDkEIwR66/Gbp0t3+r yQzpKRyQif3OwE0ETVkGzwEIALyKDN/OGURaHBVzwjgYq+ZtifvekdrSNl8TIDH8g1xicBYp QTbPn6bbSZbdvfeQPNCcD4/EhXZuhQXMcoJsQQQnO4vwVULmPGgtGf8PVc7dxKOeta+qUh6+ SRh3vIcAUFHDT3f/Zdspz+e2E0hPV2hiSvICLk11qO6cyJE13zeNFoeY3ggrKY+IzbFomIZY 4yG6xI99NIPEVE9lNBXBKIlewIyVlkOaYvJWSV+p5gdJXOvScNN1epm5YHmf9aE2ZjnqZGoM Mtsyw18YoX9BqMFInxqYQQ3j/HpVgTSvmo5ea5qQDDUaCsaTf8UeDcwYOtgI8iL4oHcsGtUX oUk33HEAEQEAAcLAXwQYAQIACQUCTVkGzwIbDAAKCRAWmrexpM/4rrXiB/sGbkQ6itMrAIfn M7IbRuiSZS1unlySUVYu3SD6YBYnNi3G5EpbwfBNuT3H8//rVvtOFK4OD8cRYkxXRQmTvqa3 3eDIHu/zr1HMKErm+2SD6PO9umRef8V82o2oaCLvf4WeIssFjwB0b6a12opuRP7yo3E3gTCS KmbUuLv1CtxKQF+fUV1cVaTPMyT25Od+RC1K+iOR0F54oUJvJeq7fUzbn/KdlhA8XPGzwGRy 4zcsPWvwnXgfe5tk680fEKZVwOZKIEuJC3v+/yZpQzDvGYJvbyix0lHnrCzq43WefRHI5XTT QbM0WUIBIcGmq38+OgUsMYu4NzLu7uZFAcmp6h8g Organization: Linaro In-Reply-To: <054ef52478fc93fc213a9dae23ea77f73094aaf2@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260930_150203_551667_1A4C42DB X-CRM114-Status: GOOD ( 29.31 ) 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: , Reply-To: Neil Armstrong Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 9/29/26 11:03, 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. Yes we could have a similar panel-simple but with init tables, but in reality those panels offers much more features we don't handle because the DDIC vendors and panel integrators just don't care exposing those features, but they get handled by vendor implementation like for Phones. > > 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. I don't think we want this, downstream vendors does that and we don't want to go there. > > Where that falls short, you could always have a dedicated driver, or > extend the declarative stuff. > > Now, the question is, how much more BPF solves over that, without > requiring a dedicated driver, and is the added complexity worth it? This is my global question, and this is what I'm evaluating here, and so far is created more problem that solutions. > > 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. For _some_ panels, here, as a general solution no because we really want to have full support for panel features. Neil > > > BR, > Jani. > >