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 DF8F24B1CF7; Thu, 17 Sep 2026 10:05:01 +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=1789639514; cv=none; b=M71GtIcWGnnxf66k8OhVotTo1u4w+YzbOdN3gNNi7yOnUFYj6OthFfJi3P9+syeAcbsz33Ldiyj/eRDfOCm+qeZhhRQFnM/WvN+ui7K8IF/1jLpA7KPzQJ3GkZ+EOniVQnnhU/EYPChROzHya6a2akxlWzTQg8L4DemGlo7UO10= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789639514; c=relaxed/simple; bh=8twaT9zLI/VWKHo/Ti18avE0HnBxOYc5otwq7psWXaI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gmsT6D+9mw87m0h5r9m4u+WJoV1CeF/AUBDD/gFpmMsmQd/u+8Dn2Hv8wY5s/Dv6scK3biyzAmGt0JK9V6c7qTXZ8KWa2BnxoAGpWhPjolLXP/Tqng/u6gvGhuJcxDaULm8n/g9TZTeT6dDTmDvIp9b77UcfQLUHe4PoNW30h70= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c6yP7X8Q; 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="c6yP7X8Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1760A1F000FF; Thu, 17 Sep 2026 10:04:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789639499; bh=Jbm4chty2zYyyLMXqcWCL6EkoK03pWrHLt0hOsiDGns=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=c6yP7X8Q0UqQoGqQHlZEAfYr2HaADgEEOz9Hc8hhZj6Kt13UlDqvEVSzH5lGPysqt UeR8nBuHUktjqDP4q8d0ZHOMOavagMRkvKbM08AdhgOqfJQHqv4h1MONi7bn0rhPCL /ygclqhTvcqwrKDbdqy/ovrpb27tuazxIPS3s+Fvea31QBpkz1u9bfh0y472KHPZ53 NVATpWWa9Zl2CcuHu8gDJ54kH/4qyMidW23idvEzLwbWbwEnenbhgOr6ITXYwzctC+ uL7GqhlVRU8qUHVRVZTwq3VUCOQ4phsX1CQOiDLXaC1d+Uqc9lUCOzoabi7j5D13kY jzIvRLjRHCIkQ== Date: Thu, 17 Sep 2026 11:04:55 +0100 From: Lee Jones To: Benjamin Tissoires Cc: Linus Walleij , Michael Zaidman , jikos@kernel.org, brgl@kernel.org, linux-input@vger.kernel.org, linux-gpio@vger.kernel.org, linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/13] HID: ft260: add UART and GPIO support, plus I2C fixes Message-ID: <20260917100455.GG1605367@google.com> References: <20260827205116.GJ2943942@google.com> <20260827222550.24634-1-michael.zaidman@gmail.com> <20260916125806.GR11487@google.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, 17 Sep 2026, Benjamin Tissoires wrote: > On Sep 16 2026, Lee Jones wrote: > > On Mon, 14 Sep 2026, Linus Walleij wrote: > > > > > Hi Benjamin, Lee, > > > > > > On Tue, Sep 1, 2026 at 4:03 PM Benjamin Tissoires wrote: > > > > > > > TBH, I'm not a big fan of having multiple subsystems children into HID. > > > > Mostly because I can't review the best practive in each of them. However, > > > > for quite a long time, HID was mostly for input devices, and input is a > > > > different subsystem. > > > > > > > > That being said, there are 2 types of HID devices: > > > > - ones with defined standard usages (keyboards, mice, touchscreen, > > > > battery, etc) and using MFD for those would certainly be overthinking > > > > - others use raw HID device with a custom protocol (cp2112, mcp2221, > > > > ft260), these could be MFD candidates > > > > > > Surely, as HID start to attract chips which clearly fall into the MFD > > > category of things, with a plethora of subsystems hooking into the > > > same HID device, we must find a way for HID devices to spawn > > > MFD cells? > > > > > > MFD solved and evolved a system for handling exactly this type > > > of situation. > > > > > > Whether there should be an MFD device in the middle spawning > > > each a HID, GPIO, I2C, UART cell or whether HID device itself should > > > sit in the nexus and gain the ability to simply spawn out MFD cells > > > from itself is what we need to figure out. > > > > There's no figuring that part out. > > > > If you want to use the MFD API, the part that uses it must reside in > > drivers/mfd. Else it becomes a nightmare to maintain and things get > > wild, quickly. > > Historically speaking, HID devices always have been under drivers/hid. > They are usually leaf drivers, only hooking to input/battery/LEDs. > > As mentioned, hid-sensor-hub is an exception but this got sorted out by > splitting the HID part from the IIO. > > Looking at the various MFD-like HID drivers, they all share the common > point of not really being HID devices: they rely on a custom protocol > handled in .raw_event(). > > So I think I'd be OK to have those drivers moved to the mfd tree as long > as they only rely on low level HID API, and do not have to deal with > "generic" HID report descriptors. If that arise, I think we should split > the HID/MFD parts like hid-sensor-hub does. > > So you can have my unformal acked-by for transfering those drivers. A couple of caveats to this: Only the most basic set-up parts need to go into MFD (shared resource allocation, core device initialisation: clocks, resets, regulators, IRQs, etc. Anything that does a 'thing' needs to reside in the applicable sub-system that supports the 'thing'. Device need to straddle at least 2 additional subsystems to qualify as an MFD which undoubtibly would be HID and then something else: gpio, regulator, uart, iio, clk, what have you. > Last, I'm currently using a cp2112 as a i2c-hid bridge in my upstream > CI. It's relying on a DSDT override in the VM to actually work, and I'd > like to keep that around. So my main request here is to keep the > equivalent of the DSDT override in the MFD cells, at least for this one. I have no idea what that means, but we can discuss it. Maybe this lives in some form of platform data? I'd be able to advise better when I know what it is. -- Lee Jones