From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Preston Subject: Re: [PATCH v2] Documentation: acpi: Add an example for PRP0001 Date: Mon, 25 Mar 2019 16:52:05 +0000 Message-ID: <2ccd44f4-5f5b-60db-d002-3f33dfcdd321@codethink.co.uk> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190325163423.GJ9224@smile.fi.intel.com> Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: linux-acpi@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