linux-kernel - Re: [PATCH RESEND v3 1/6] i3c: mipi-i3c-hci: Add MIPI0100 ACPI ID to the I3C Support List

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Message-ID: <c6ef0253-9f32-46d6-a658-295e39c926b2@amd.com>
Date: Fri, 9 Aug 2024 21:02:35 +0530
From: Shyam Sundar S K <Shyam-sundar.S-k@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Guruvendra Punugupati <Guruvendra.Punugupati@....com>,
 Krishnamoorthi M <krishnamoorthi.m@....com>, linux-i3c@...ts.infradead.org,
 linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH RESEND v3 1/6] i3c: mipi-i3c-hci: Add MIPI0100 ACPI ID to
 the I3C Support List

On 8/9/2024 19:48, Andy Shevchenko wrote:
> On Fri, Aug 09, 2024 at 04:54:18PM +0300, Jarkko Nikula wrote:
>> Hi
>>
>> I Cc'ed Andy and Rafael because of ACPI ID allocation question that came to
>> my mind below which I'm not expert enough to answer.
>>
>> On 8/7/24 8:23 AM, Shyam Sundar S K wrote:
>>> The current driver code lacks the necessary plumbing for ACPI IDs,
>>> preventing the mipi-i3c-hci driver from being loaded on x86
>>> platforms that advertise I3C ACPI support.
>>>
>>> This update adds the MIPI0100 ACPI ID to the list of supported IDs.
> 
> When adding a new ACPI ID, always provide the following information:
> 
> 1) link (in some form) to the official confirmation / documentation for
> the allocated ID by the vendor (MIPI in this case) _OR_ (very exceptional!)
> why the bad ID had been allocated;

Member version:
https://members.mipi.org/wg/All-Members/document/previewpdf/89465

Public version: https://www.mipi.org/mipi-disco-for-i3c-download (this
requires a signup).

Since there is no direct link available for preview, I did not include
them in the commit-msg. But left a note that the MIPI ID is the one as
specified in the MIPI DisCo spec.

> 
> 2) are there devices in the wild (on the market) that use the being added ID(s)?
> 

Not in the wild. But the latest platform will have this support
included. So, these device IDs are crucial for the i3c-hci to be
supported on AMD platforms.

> 3) excerpt from the device (independently if it's public already, see above,
> or not) DSDT ACPI table.
> 
> With the given patch it looks to me that you most likely need a local, AMD
> specific ID as well.
> 
> So, in my ideal world the DSDT should be like
> 
> 	Device (I3CC)
> 	{
> 		Name (_HID, "...") // AMD specific _HID
> 		Name (_CID, "MIPI0100") // Compatible ID for generic I3C controller
> 		...
> 	}
> 
> Is this the case? Why not?

Please refer to the MIPI HCI I3C DisCo specification
(https://members.mipi.org/wg/All-Members/document/previewpdf/89465)
section 5.4. The ASL looks the same in case of AMD.

MSFT says that they want to use MIPI0100 as mentioned in the
specification.

What would you advise?

> 
> P.S. Make sure you Cc me on ACPI ID matters in the future.
> 

Sure, will do.

Thanks,
Shyam