linux-kernel - ACPI binding with SCMI

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Message-ID: <CH0PR02MB80732F4C4134B3EF2D80B4EDF6E3A@CH0PR02MB8073.namprd02.prod.outlook.com>
Date:   Fri, 25 Aug 2023 21:34:59 +0000
From:   "Pawandeep Oza (QUIC)" <quic_poza@...cinc.com>
To:     'Sudeep Holla' <sudeep.holla@....com>,
        "rafael@...nel.org" <rafael@...nel.org>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: ACPI binding with SCMI

Hi Sudeep,

I have PCC based regions defied in ACPI, and CPPC binding already exists through _CPC and all the way in kernel to facilitate per control.

I am looking at SCMI on ACPI based systems - and I am going through kernel source, SCMI specification.
spec mentions
"The SCMI transport is represented as a standard ACPI Platform Communications Channel (PCC) of Type 3. SCMI transports that follow the format outlined in section 5.1 are compatible with PCC type 3 channel definition. Also, ACPI version 6.3 introduces the concept and use of PCC operation regions. This enables ACPI methods that rely on underlying SCMI services to access the SCMI transport through PCC operation regions."

But when I look at kernel source: drivers/firmware/arm_scmi  -> mailbox_chan_setup is just reading the information from device tree.

https://lore.kernel.org/lkml/MN2PR18MB3358B61B4B5777FB35B42733BA3A9@MN2PR18MB3358.namprd18.prod.outlook.com/T/
you have outlined the way to have SCMI bind to PCC space in above thread

"
However, being aware of this difference, and also for other valid requirements
we introduced the concept of Fastchannels in SCMI for performance protocol
mainly to bypass the PCC/mailbox overhead. It also aligns well with CPPC.
You just need to implement fastchannels in SCMI and specify those as
system memory GAS instead of PCC GAS in CPPC tables. Hope that helps, happy
to provide more details once you get familiarised with SCMI Fastchannels.
"

But I still fail to see how fastchannel doorbell and shared memory space could get bind to PCC space (type 3) ? I am on 6.3 kernel.

Regards,
Oza.