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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 68C2DC43381 for ; Mon, 25 Mar 2019 16:52:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4201120863 for ; Mon, 25 Mar 2019 16:52:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729548AbfCYQwJ (ORCPT ); Mon, 25 Mar 2019 12:52:09 -0400 Received: from imap1.codethink.co.uk ([176.9.8.82]:38094 "EHLO imap1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725788AbfCYQwJ (ORCPT ); Mon, 25 Mar 2019 12:52:09 -0400 Received: from [167.98.27.226] (helo=[10.35.5.150]) by imap1.codethink.co.uk with esmtpsa (Exim 4.84_2 #1 (Debian)) id 1h8SpS-0000O4-KH; Mon, 25 Mar 2019 16:52:06 +0000 Subject: Re: [PATCH v2] Documentation: acpi: Add an example for PRP0001 To: Andy Shevchenko Cc: rjw@rjwysocki.net, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, mika.westerberg@linux.intel.com References: <20190325151210.23226-1-thomas.preston@codethink.co.uk> <20190325153032.GG9224@smile.fi.intel.com> <3ae33d42-1175-bdbe-036b-1df5edc6a802@codethink.co.uk> <20190325163423.GJ9224@smile.fi.intel.com> From: Thomas Preston Message-ID: <2ccd44f4-5f5b-60db-d002-3f33dfcdd321@codethink.co.uk> Date: Mon, 25 Mar 2019 16:52:05 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190325163423.GJ9224@smile.fi.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/03/2019 16:34, Andy Shevchenko wrote: > On Mon, Mar 25, 2019 at 03:58:13PM +0000, Thomas Preston wrote: >> On 25/03/2019 15:30, Andy Shevchenko wrote: >>> On Mon, Mar 25, 2019 at 03:12:10PM +0000, Thomas Preston wrote: >>>> Add an example for the magic PRP0001 device ID which allows matching >>>> ACPI devices against drivers using OF Device Tree compatible property. >>> >>>> It wasn't clear to me that PRP0001 could be used in _CID. >>> >>> Yes, but it's not necessary to have it if we have defined a _HID. >>> >>> In that case PRP0001 is a temporary stub until corresponding driver >>> incorporates an official _HID. >>> >>> On the contrary, when there is no official _HID available, PRP0001 can be used >>> instead directly as a _HID and no _CID is needed. >>> >> >> In that case, how do we uniquely identify devices in sysfs? > > By their class, etc. > > Identifying devices based in instance name is bad idea to start with. > >> We have a >> case where sound/soc/soc-core.c generates an i2c codec name i2c-TDA7802:00. >> It is useful to identify that device by part name, rather than some indexed >> generic PRP device i2c-PRP0001:04. I can achieve this with: > > If TDA7802 is *official* _HID dedicated for that codec by vendor, add it to the > driver... > >> _HID("TDA7802") > >> _CID("PRP0001") >> ... >> compatible = "st,tda7802" // driver I want to load using OF DT > > ...and these lines become unneeded. > > The only case when both are needed is a time between one gets a case and actual > ID appears in the upstream driver. Effectively means product developing stage. > > P.S. Yes, I know that sometimes the platform/BIOS vendors abuse specification > and ACPI ID registry and made up IDs, in that case we need to support them as a > "de facto" quirks. > > And yes, ASoC subsystem in ACPI case abuses Linux device hierarchy by matching > by instance instead of matching by let say fwnode. It should be fixed there, > not in ACPI table. > Okay this is all really useful information. Thank you. >> >>> I would really recommend to look at the examples in meta-acpi repository. There >>> are cases like described above. >>> >>> This one is good enough, though see below. >>> >> >> I will drop the superfluous _CID - I think the example is still useful >> to have. Even if we don't illustrate my special case for _HID/_CID. > > Yes, I agree with that. > I will remove _CID weirdness, and resend. I will deal with my special case elsewhere. Thanks again