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 5CDC5C433EF for ; Wed, 16 Feb 2022 17:33:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237110AbiBPRdV (ORCPT ); Wed, 16 Feb 2022 12:33:21 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:36282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237097AbiBPRdT (ORCPT ); Wed, 16 Feb 2022 12:33:19 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1A6922128B6; Wed, 16 Feb 2022 09:33:07 -0800 (PST) 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 AB4C861BC5; Wed, 16 Feb 2022 17:33:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 809BCC340E8; Wed, 16 Feb 2022 17:33:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1645032786; bh=qYYdvT6AeCXuOfXWgf9Vb2nVM8/mVSQ3AS/PSeriAhM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lQyWt24JhOIOrw2z1XZlLZ4AShWBTjF+Mw2U+/MzBIfagEq1m1oNJSnB+xFjo9wcr Uq9a8jKVsSvykveWdQSApN+8pHaQI3OTX6RPAP22fW7kpYyS5JiPxHFVWTsaVpW7EQ hTvzjDTJ+aftNgohE2CTeMTuDtTl8DJNCBUzfvyc= Date: Wed, 16 Feb 2022 18:33:02 +0100 From: Greg Kroah-Hartman To: "Rafael J. Wysocki" , Won Chung , Len Brown , Heikki Krogerus , Benson Leung , Prashant Malani Cc: ACPI Devel Maling List , Linux Kernel Mailing List Subject: Re: [PATCH v6] ACPI: device_sysfs: Add sysfs support for _PLD Message-ID: References: <20220211023008.3197397-1-wonchung@google.com> 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, Feb 15, 2022 at 03:04:54PM +0100, Rafael J. Wysocki wrote: > Adding Greg, who should be involved in this discussion IMO. > > On Mon, Feb 14, 2022 at 11:59 PM Won Chung wrote: > > > > On Mon, Feb 14, 2022 at 12:30 PM Won Chung wrote: > > > > > > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki wrote: > > > > > > > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung wrote: > > > > > > > > > > When ACPI table includes _PLD fields for a device, create a new > > > > > directory (pld) in sysfs to share _PLD fields. > > > > > > > > This version of the patch loos better to me, but I'm not sure if it > > > > goes into the right direction overall. > > > > > > > > > Currently without PLD information, when there are multiple of same > > > > > devices, it is hard to distinguish which device corresponds to which > > > > > physical device in which location. For example, when there are two Type > > > > > C connectors, it is hard to find out which connector corresponds to the > > > > > Type C port on the left panel versus the Type C port on the right panel. > > > > > > > > So I think that this is your primary use case and I'm wondering if > > > > this is the best way to address it. > > > > > > > > Namely, by exposing _PLD information under the ACPI device object, > > > > you'll make user space wanting to use that information depend on this > > > > interface, but the problem is not ACPI-specific (inevitably, it will > > > > appear on systems using DT, sooner or later) and making the user space > > > > interface related to it depend on ACPI doesn't look like a perfect > > > > choice. > > > > > > > > IOW, why don't you create a proper ABI for this in the Type C > > > > subsystem and expose the information needed by user space in a generic > > > > way that can be based on the _PLD information on systems with ACPI? > > > > > > Hi Rafael, > > > > > > Thank you for the review. > > > > > > I was thinking that _PLD info is specific to ACPI since it is part of > > > the ACPI table. Could you explain a little bit more on why you think > > > exposing _PLD fields is not an ACPI-specific problem? > > _PLD is an interface defined by ACPI, but its purpose is not ACPI-specific. > > > Hi Rafael again, > > > > Sorry for the silly question here. I misunderstood your comment a bit, > > but I talked to Benson and Prashant for clarification. I understand > > now what you mean by it is not an ACPI-specific problem and exposing > > PLD would depend on ACPI. > > Right. > > > > > > > I gave an example of how _PLD fields can be used for specifying Type C > > > connectors, but it is not Type C specific. For Chrome OS, we plan to > > > initially add PLD to not only Type C connectors but also USB port > > > devices (including Type C and Type A). Also, PLD can be used in the > > > future for describing other types of ports too like HDMI. (Benson and > > > Prashant, please correct or add if I am wrong or missing some > > > information) Maybe my commit message was not detailed enough.. > > > > > > I am also curious what Heikki thinks about this. Heikki, can you take > > > a look and share your thoughts? > > > > I am still curious what you and Heikki think about this since it may > > not be a Type C specific issue. We can start from adding generic > > location info to Type C subsystem first, as you suggested, then > > consider how to do the same for USB devices and Type A ports > > afterwards. I would appreciate sharing any thoughts or feedback. Thank > > you very much! > > I don't really think that this is a Type C problem either. > > It has existed for a long time in the USB world, for example, or > wherever there are user-accessible ports, but it looks like in the > Type C case it has become vitally important. > > My point is that writing user space depending on accessing _PLD > information exposed under an ACPI device interface that only > corresponds to the device in question and in the ACPI-specific format > would be a mistake (Greg, please let me know if you disagree). That's > because (a) it would depend on ACPI tables being present (so it > wouldn't work on systems without them) and (b) it would depend on the > format of data which covers information that isn't likely to be > relevant. > > If this information is exposed by the kernel verbatim and user space > depending on this information is created, it will not be possible to > unexpose it even if it turns out that exposing it has been a mistake. > > OTOH, if only the relevant pieces of information are exposed in a > generic way, it is always possible to expose more pieces of it in the > future as needed. There are pending patches on the linux-usb mailing list from Heikki to help expand on the typec information in sysfs in a generic way. Won, please work with the linux-usb developers on this change and do not do anything that is ACPI-specific and only. That way will not be good for anyone involved. Please see: https://lore.kernel.org/r/20220203144657.16527-1-heikki.krogerus@linux.intel.com for the current discussion. thanks, greg k-h