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 7521C3BF68F; Thu, 17 Sep 2026 11:07:51 +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=1789643283; cv=none; b=hXJ4+7zYZg9VB6AMJSQaItknmYJRFGXRP3Uin0ZfG5vO1fn4MiMObyd/jB4u+36JhupT1d0AhW7YYwQDUsTX6MsFsRdGrG7Vc/ATUEzfBe7vmW3c8Oq3qFb5AQny0+T5ZmPLmKqNGmrm7OQ3rvhhXcRAZHIpjNIDR1d+ktWnp9w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789643283; c=relaxed/simple; bh=UqDznbQQYvwxszCrE1RJLK+ZSAl3k1Y7zKbb9JwSGyQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=i4wXKDUthxuTBcwVJtGFwsvwNrXwP4FEViduMwIbrCUR+e/lDafQv8VLYK0Ro4wP/AtCq4wr5PsmGrGyHuwPGVlSKRrtpRssCNnoSd3drYK63Tqm8s4ygVJe2OJWMIB7JVzcl0y/+zSt0ojXpTiIt+GBcVXHTYt1YIJwyZ3Djlg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OvF9yQd7; 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="OvF9yQd7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 458CC1F000FF; Thu, 17 Sep 2026 11:07:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789643267; bh=SnIYJHQj1Hi2CtUKuIOZa/edUAelnTSBug0kHw/k7+0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=OvF9yQd7ANSPZlDG/sWvuTnz7rI2x1eo0WCdXrJ9UbyEziUnPWG0nGajKgsISil3Y 2eYYIrjI8f+QxeobRu2uPKQKA7J35NNws89bt3LdLA67OQqTDBGhN7gkBuvIqFwsmH sEoQGxyzYAE+IcN4RefiJBLTlcZ4RUdwl5qmyL02WYRQsDwpXXMUCx/0zYShtrOoL6 /+CuDG9sQm4aonEKFt+YDOdrWsOlndmNIu2fg0UShf3dDkQhkmpt1n3nYehGhokOkD OBXgtSD0q+7kAzCxUfmxK39G3lMa71xYxOjBMxSBhjOjFXNFxLeZNNpeO69+5uG6F7 HyFvQmX3tSxfQ== Date: Thu, 17 Sep 2026 13:07:42 +0200 From: Benjamin Tissoires To: Lee Jones 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: References: <20260827205116.GJ2943942@google.com> <20260827222550.24634-1-michael.zaidman@gmail.com> <20260916125806.GR11487@google.com> <20260917100455.GG1605367@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: <20260917100455.GG1605367@google.com> On Sep 17 2026, Lee Jones wrote: > 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'. Sure, as long as I'm not responsible for those :) > > 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. I think HID is just the transport layer (like USB, I2C, SPI, etc...) so it shouldn't count as one of the additional subsystems to MFD. > > > 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. I apply the following DSDT to the VM that is running the test device: https://gitlab.freedesktop.org/bentiss/gitlab-kernel-ci/-/blob/master/VM/0004-Add-CP2112-SSDT-override.patch?ref_type=heads#L51 Basically, this converts the CP2112 from being a simple USB device to a known I2C + GPIO device by the ACPI table, and where I can then attach another I2C child device (Device (TPD0) in the DSDT). It's the same than adding a device tree to a platform where the I2C bus is connected to a USB bus but is soldered on the chip. My only constraint here is that the children of the MFD node properly have the fwnode support. See commit c0be05f68a21 ("HID: cp2112: Add fwnode support") for when this was added upstream. I would assume MFD correctly sets fwnodes for the children devices it handles, and hopefully it's working fine with ACPI as well. Cheers, Benjamin