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: <Zrn9ZLEMVGm2e1Db@smile.fi.intel.com>
Date: Mon, 12 Aug 2024 15:17:40 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: Shyam Sundar S K <Shyam-sundar.S-k@....com>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.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 Fri, Aug 09, 2024 at 08:39:40PM +0200, Alexandre Belloni wrote:
> On 09/08/2024 18:57:04+0300, Andy Shevchenko wrote:
> > > 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.
> 
> Just to be clear, the HCI defines the register interface to the IP but
> not the IP itself, this is just like the various USB and SD HCIs.

Thank you for this elaboration, it's a crucial aspect!

> So we will definitively see quirks as implementers will interpret the
> interface differently

With the above remark this makes a lot of sense.

> (and so I agree with everything that was said ;) )

> > 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)"
> > 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.

-- 
With Best Regards,
Andy Shevchenko