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([2a01:e0a:106d:1080:2f62:6d3:721b:8c9e]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48b38104e07sm3611058f8f.31.2026.10.02.00.30.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Oct 2026 00:30:10 -0700 (PDT) Message-ID: <2bd17843-4a65-49b0-9e10-7b73afb206b6@linaro.org> Date: Fri, 2 Oct 2026 09:30:09 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Neil Armstrong Reply-To: Neil Armstrong Subject: Re: [PATCH 0/6] drm/bridge: Add a BPF-based MIPI-DSI panel driver To: Maxime Ripard Cc: Javier Martinez Canillas , Benjamin Tissoires , 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 , 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 References: <20260928-drm-mipi-dsi-panel-ebpf-v1-0-5244926aace4@kernel.org> <6b80cb97-6706-412a-b013-9423f6f75153@linaro.org> <0259fe4b-3118-4ab0-9b62-55101bfd7f33@linaro.org> <674314b4-6b80-4b3a-ac15-eefd31cea607@linaro.org> <828c9108-2db1-45a6-9301-19159a094301@linaro.org> 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/1/26 08:50, Maxime Ripard wrote: > On Wed, Sep 30, 2026 at 03:37:58PM +0200, Neil Armstrong wrote: >> On 9/29/26 09:55, Javier Martinez Canillas wrote: >>> Maxime Ripard writes: >>> >>>> On Mon, Sep 28, 2026 at 10:36:18PM +0200, Neil Armstrong wrote: >>>>> On 9/28/26 21:48, Benjamin Tissoires wrote: >>>>>> On Sep 28 2026, Neil Armstrong wrote: >>>>>>> On 9/28/26 19:24, Benjamin Tissoires wrote: >>>>>>>> On Sep 28 2026, Neil Armstrong wrote: >>>>>>>>> Hi, >>>>>>>>> >>>>>>>>> On 9/28/26 18:22, 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. >>>>>>>>> >>>>>>>>> This is kind of late for serious applications except if we manage to >>>>>>>>> solve the bootloader to Linux display engine transition. >>>>>>>>> >>> >>> Besides what Maxime already mentioned (that most general purpose Linux distributions >>> built the drivers as modules anyways), it doesn't have to be mutually exclusive. >>> >>> A simple panel could be supported using this BPF-based driver and then a panel driver >>> added to the kernel, if is found that some applications need to have it built-in and >>> earlier in the boot path. >>> >>> I don't see why this would be any different than HDI-BPF or other BPF-based infra, >>> such as sched_ext. >> >> I don't want to add a supplementary maintenance burden for the sake of using a cool >> technology which has serious drawbacks and dependencies on user-space even if looks >> really cool. > > Spoiler alert: v2 won't. I've got the in-kernel loader to work and thus > you can have a built-in panel driver that works without user-space > intervention. So this is not a topic of discussion anymore. It will still have users-space dependency, meaning the BPF files will need to exist in the fs when drivers probes. Neil > > Maxime > > > will work