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 20ADAC00144 for ; Fri, 29 Jul 2022 17:15:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237977AbiG2RPc (ORCPT ); Fri, 29 Jul 2022 13:15:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237951AbiG2RPa (ORCPT ); Fri, 29 Jul 2022 13:15:30 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BD797B7C5 for ; Fri, 29 Jul 2022 10:15:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3F3CE61EF2 for ; Fri, 29 Jul 2022 17:15:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 40DB0C433D6; Fri, 29 Jul 2022 17:15:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1659114927; bh=VAkEGQMytpddlsQ64xfJjyOEeyWtSq4kkkEs8HNbh64=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=t+jw/oEvzQ0ZS7d4yPWHfkE5ZHKpFe7S0xEGGznHHgssCeJ3xgB9KSWWVWJCujN9A 2sHRVGnfsZfr2yJhE9BOdyuSbzIfoC+ZhfYLmlqM1P26pF6lbzIwFizPma1tNUsrmL ijDjWmXEXDkDJSiQpIJMzYGqoTLujQ3bDBW4PGMI= Date: Fri, 29 Jul 2022 19:15:24 +0200 From: Greg Kroah-Hartman To: Pierre-Louis Bossart Cc: Vinod Koul , alsa-devel@alsa-project.org, Bard Liao , linux-kernel@vger.kernel.org, Sanyog Kale Subject: Re: [PATCH 2/5] soundwire: sysfs: cleanup the logic for creating the dp0 sysfs attributes Message-ID: References: <20220729135041.2285908-1-gregkh@linuxfoundation.org> <20220729135041.2285908-2-gregkh@linuxfoundation.org> <9365e038-2146-98f8-f989-02827f221c34@linux.intel.com> <5caffe2a-f5a6-e312-a564-5fe29c4e2323@linux.intel.com> <701aa1ba-9b25-51eb-8bd7-2389b501d79c@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <701aa1ba-9b25-51eb-8bd7-2389b501d79c@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 29, 2022 at 11:46:32AM -0500, Pierre-Louis Bossart wrote: > > >>>>> That should be fine, tools should just be looking for the attributes, > >>>>> not the existance of a directory, right? > >>>> > >>>> The idea what that we would only expose ports that actually exist. > >>>> That's helpful information anyone with a basic knowledge of the > >>>> SoundWire specification would understand. > >>> > >>> Is "dp0" a port? If so, why isn't it a real device? > >> > >> The SoundWire spec defines the concept of 'data port'. The valid ranges > >> are 1..14, but in all existing devices the number of data ports is way > >> smaller, typically 2 to 4. Data ports (DPn) are source or sink, and > >> there's no firm rule that data ports needs to be contiguous. > >> > >> DP0 is a 'special case' where the data transport is used for control > >> information, e.g. programming large set of registers or firmware > >> download. DP0 is completely optional in hardware, and not handled in > >> Linux for now. > >> > >> DP0 and DPn expose low-level transport registers, which define how the > >> contents of a FIFO will be written or read from the bus. Think of it as > >> a generalization of the concept of TDM slots, where instead of having a > >> fixed slot per frame the slot position/repetition/runlength can be > >> programmed. > >> > >> The data ports could be as simple as 1-bit PDM, or support 8ch PCM > >> 24-bits. That's the sort of information reported in attributes. > > > > Why not make them a real device like we do for USB endpoints? > > I don't see what adding another layer of hierarchy would bring. In their > simplest configuration, there are 6 registers 8-bit exposed. And the > port registers, when present, are accessed with a plain vanilla offset. Who uses these registers? > > What uses these sysfs files today that would be confused about an empty > > directory? > > That's a good question. I am not aware of any tools making use of those > attributes. To a large degree, they are helpful only for debug and > support, all these read-only attributes could be moved to debugfs. That > could be a way to simplify everyone's life.... That would be much nicer, put it all in a single debugfs file and it would be so simple. What attributes could we do that for? thanks, greg k-h