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Fri, 14 Aug 2026 12:13:26 -0700 (PDT) Received: from google.com ([2a00:79e0:2ebe:8:e0b1:a24a:3d2a:2ee9]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-320ea2f787fsm6880832eec.20.2026.08.14.12.13.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Aug 2026 12:13:24 -0700 (PDT) Date: Fri, 14 Aug 2026 12:13:22 -0700 From: Dmitry Torokhov To: Evan Lawrence Cc: linux-input@vger.kernel.org, linux-api@vger.kernel.org, miroslav.bendik@gmail.com Subject: Re: [PATCH v5] Input: synaptics - add pass-through mode for TrackPoint Message-ID: References: <20260810142440.9060-1-development@laserology.net> Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260810142440.9060-1-development@laserology.net> Hi Evan, On Mon, Aug 10, 2026 at 02:25:03PM +0000, Evan Lawrence wrote: > Synaptics touchpads with a pass-through port (PS/2 guest) default to > encapsulating guest data in the touchpad's own packets, limiting the > guest device (typically a TrackPoint) to the touchpad's low poll rate. > Enabling transparent pass-through mode tells the touchpad to stop > generating its own packets and relay the raw byte stream from the guest > directly, letting the TrackPoint run at its full native speed while the > touchpad is effectively disabled. > > This reworks an earlier implementation by Miroslav Bendík from 2022 > that was never merged. It keeps the same hardware-mode approach but > commits the mode flag only after a successful mode command, moves the > reconnect handling into a generic psmouse hook instead of protocol- > specific checks in psmouse-interrupt, and documents the interface. > > The mode is exposed via a sysfs transparent_mode attribute that allows > userspace to switch between full-rate TrackPoint and full-rate touchpad > operation at runtime. > > If the system warm-boots while transparent mode is active the touchpad > stays in that mode and does not acknowledge command bytes, so > ps2_command() hangs and the device fails to be detected. Escape > transparent mode by writing SETSCALE21 + SETSCALE11 directly to the wire > with serio_write() before attempting a reset or probe, both during > initial detection and on reconnect. 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)? Thanks. -- Dmitry