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bh=lc0rq7xR25Ol7sYvMYnfF2oc0o89SQWS3k7iGuZjJ8I=; b=GiJeo+I/BoF3oCsWP3rcVNHRyXlOWvoIdPFZT5DNT0W34GLqxEfhdgl00nCyipWeehCS9a mYNrw3xUmvquyuXN8tW8EYlA6KkoQy17vxHDF0NLeudcsn8Oix7R/YoIopd48nbkSgZ+wj +21Og8MgbWovZvVGGhOV2SLznPZsT2q101VGZly6pfKWlV/aIVYQYrPgC6peCdj1XPsJDf xxAxIJbq76fH3RrA678ZHU/+wi0yTa/6d/qGEwz4NH9pykBeU5yjSHqGZQwt92nBModJoa s5v4n0X8Kb8BTJRXCU2xEdJWW8Te7Ufs/XiZBnq09A8vOvlQndZWGxraSARfSw== From: Evan Lawrence To: dmitry.torokhov@gmail.com Cc: development@laserology.net, linux-api@vger.kernel.org, linux-input@vger.kernel.org, miroslav.bendik@gmail.com Subject: Re: [PATCH v5] Input: synaptics - add pass-through mode for TrackPoint Message-ID: <20260815004214.68767-1-development@laserology.net> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Date: Sat, 15 Aug 2026 00:42:40 +0000 (UTC) X-CM-Envelope: MS4xfHF7PoVelKQNVpgYwJwKsRbtshPavORooC9iaHbKTqHDbaDZWM0BOwN9SoOIaxPuEuO7w7NpmruUBpxy5cVU67d3mGesR9tkR0gCZK+ROXLrltmw3ToJ His5lypjVA0l/ND8jAjYkNkGoLkOWZH4BIilqABqBkTD0V/r5BC/XSkwUe3O8FXqmH+F7cHY4654SYDDS6/c1YOvN8y+EaSxSnV1t4VOp0fujOO6ZtBl9ln3 lnQJ9IcEbDG4vur1fsRtoiGHc0W6raUDaEc3q/PaeSOmCXX1SPzyDh5cEnwTMRIvnj4TwDAvn4bM3hHxhvFn7agGEI23oz10gpfmdCaU+llPw6Ca/5/P1k95 p/43IjgwpPs4E9Kne0kNrjotaLBsBo+INd9/ygwqYRnltgMZ/j4Wzd+ExTLu/+d/C2M49Oz4 X-CM-Analysis: v=2.4 cv=V5Av0vni c=1 sm=1 tr=0 ts=6a7fb602 a=bXe6bw2OB92olpQ1pPvang==:617 a=xqWC_Br6kY4A:10 a=0--Fi8ekQfCFXZ83AN0A:9 X-AuthUser: admin@laserology.net Hi Dmitry, On Thu, Aug 14, 2026 at 07:13:00PM +0000, Dmitry Torokhov wrote: > I have not looked at the implementation yet, just a high-level question: > > What devices need this? Can they work in SMbus/RMI4 mode instead (which > should alleviate bandwidth concerns)? The target devices are ThinkPad T14/P14s Gen 1/2-class Synaptics pass-through touchpads. The primary test hardware is a ThinkPad T14 Gen 1 (AMD), whose touchpad reports firmware id LEN2064 and whose TrackPoint is an Elan PS/2 device connected through the touchpad's pass-through port. On this device SMBus/RMI4 is not a viable alternative. Even with psmouse.synaptics_intertouch=1 forced and the touchpad re-probed, it stays in PS/2 mode (no RMI4 device is created). The touchpad's own bandwidth isn't problem; it reports at 75-85 Hz in both modes. The bottleneck is specifically the TrackPoint: behind the pass-through port it is serviced at only 35-40 Hz, but with transparent mode enabled it reaches 75-110 Hz. The exact peak rate may vary by model, but the improvement should be consistently positive. The transparent pass-through mode addresses exactly that PS/2 pass-through bottleneck by relaying the guest's raw byte stream directly instead of encapsulating it. I'll follow up with a v6 that also reduces the mode-switch latency by avoiding the ACK-waiting ps2_command() calls on the escape sequence; I will send it as soon as I have tested it. Thanks, Evan