From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B202AC3DA78 for ; Tue, 17 Jan 2023 16:01:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231302AbjAQQBx (ORCPT ); Tue, 17 Jan 2023 11:01:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230268AbjAQQBq (ORCPT ); Tue, 17 Jan 2023 11:01:46 -0500 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id BC76430B16 for ; Tue, 17 Jan 2023 08:01:43 -0800 (PST) Received: (qmail 170339 invoked by uid 1000); 17 Jan 2023 11:01:42 -0500 Date: Tue, 17 Jan 2023 11:01:42 -0500 From: Alan Stern To: Bastien Nocera Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Benjamin Tissoires , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: [RFC] USB: core: Add wireless_status sysfs attribute Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 17, 2023 at 04:17:23PM +0100, Bastien Nocera wrote: > Hey, > > TLDR: new sysfs attribute that makes it possible to leave receivers for > wireless headsets plugged in. At the USB level, or at the base driver > level? > > Longer version: > I started working on implementing support for some wireless headsets > that use USB receivers to communicate to the headset itself. > > The USB receivers have multiple interfaces, and independent drivers for > each, as is wont to do for USB devices. There's usually a HID interface > to do the custom stuff (LEDs, battery status, connection status, etc.) > and a standard audio class interface. > > Those drivers don't know anything about each other, and getting them to > talk to each other would be rather complicated. Additionally the audio > interface is still somewhat functional when the headset is > disconnected. > > In the end, I came up with this new sysfs attribute that would make it > possible for user-space (PulseAudio or Pipewire) to know whether the > receiver is plugged in or not. > > That allows user-space to not show the battery information for the > device (rather than 0 percent), not offer the headset as an output, and > potentially automatically switch to it when the headset is powered on. > > The question is whether this should be a USB sysfs attribute, or one at > the base driver level. Example implementation of the USB sysfs > attribute itself below. Do you know of any non-USB devices using the receiver/emitter approach? > I have a patch for a USB API as well, but I'm having some problems > creating deferred work on a soft irq. > > Cheers > > ---- > Add a wireless_status sysfs attribute to USB devices to keep track of > whether a USB device that uses a receiver/emitter combo has its > emitter connected or disconnected. > > By default, the USB device will declare not to use a receiver/emitter. How do you plan to tell which devices do use a receiver/emitter? Is this something the drivers already knowo about? Is it conceivable that a single device might have more than one receiver? If so, should the attribute belong to an interface rather than to the USB device? Alan Stern