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: <a48bfb06-d236-44a1-9ee6-600e63c00711@amd.com>
Date: Fri, 9 Aug 2024 21:54:52 +0530
From: Shyam Sundar S K <Shyam-sundar.S-k@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
 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 21:27, Andy Shevchenko wrote:
> On Fri, Aug 09, 2024 at 09:02:35PM +0530, Shyam Sundar S K wrote:
>> On 8/9/2024 19:48, Andy Shevchenko wrote:
>>> On Fri, Aug 09, 2024 at 04:54:18PM +0300, Jarkko Nikula wrote:
>>>> On 8/7/24 8:23 AM, Shyam Sundar S K wrote:
> 
> ...
> 
>>> 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.
> 
> It's fine.
> 
>>> 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.
> 
> Good, let's do it right then!
> 
>>> 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.
> 
> MIPI doesn't know how to assign the ACPI ID correctly. But again, what I put in
> the above is the correct way of approaching.
> 
>> What would you advise?
> 
> Since my intuition and experience tells me that the two devices even based on
> the same IP are not the same (see word 'quirk' or '.driver_data' or alike in
> the kernel sources) the generic ID may not be used for the specific vendor
> unless it's _the only_ vendor for the certain IP.
> 
> So, please do as I suggested above. And file a error report (and correction
> proposal) to the MIPI, so in "5.1 I3C Host Controller ACPI Hardware ID (_HID)"

Thank you. I shall file a error report soon to get it corrected.

> they should use _CID instead of _HID and add some text like
> "Each vendor should dedicate it's own _HID for the platform in question. The
> same _HID as _CID may be used if and only if vendor guarantees that there 100%
> compatibility with MIPI as described in this and other related documents."
> 
> I.o.w. do you 100% guarantee that MIPI HCI I3C DisCo covers all necessary
> properties that you need for _your_ hardware? If not, use my approach, if yes,
> use the same _HID *and* _CID.
> 
> Microsoft should know this as well and much better than MIPI.
> 

Agree with your thoughts. I will respin based on your remarks after
internal discussion. If it requires _HID to be MIPI0100, I will come
back with answers.

Thanks,
Shyam