linux-kernel - Re: [PATCH v24 1/1] mctp pcc: Implement MCTP over PCC Transport

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Message-ID: <d6b7d0c82806ef41bc7ee7173595d334acbf3b17.camel@codeconstruct.com.au>
Date: Mon, 18 Aug 2025 08:33:48 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Adam Young <admiyo@...eremail.onmicrosoft.com>, 
 admiyo@...amperecomputing.com, Matt Johnston <matt@...econstruct.com.au>, 
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Sudeep Holla
	 <sudeep.holla@....com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
	Huisong Li <lihuisong@...wei.com>
Subject: Re: [PATCH v24 1/1] mctp pcc: Implement MCTP over PCC Transport

Hi Adam,

> > And just confirming: the pcc header format is now all host-endian - or
> > is that a firmware-specified endianness? (what happens if the OS may
> > boot in either BE or LE? is that at all possible for any PCC-capable
> > hardware, or are we otherwise guaranteed that we're the same endianness
> > as the consumer?)
> 
> The specification does not specify endianess.  It is not addressed in
> the ACPI  PCC spec nor the MCTP over PCC spec. There does not seem  to 
> be any endianess modifiers in any of the ACPI code base.

There are a few cases of endian conversion, they appear to be cases
where a pre-defined data format is used, and only where that data is BE.

That's a pretty strong indication that we don't need to worry about host
endian != firmware endian (I'm assuming that firmware is the entity
that parses the PCC headers you're constructing). All sounds good then.

Cheers,


Jeremy