Re: [PATCH v4 0/3] MCTP over PCC

Dan Williams
2024-07-11T16:57:40Z

admiyo@ wrote:
> From: Adam Young <admiyo@os.amperecomputing.com>
>
> This series adds support for the Management Control Transport Protocol (MCTP)
> over the Platform Communication Channel (PCC) mechanism.
>
> MCTP defines a communication model intended to
> facilitate communication between Management controllers
> and other management controllers, and between Management
> controllers and management devices
>
> PCC is a mechanism for communication between components within
> the Platform. It is a composed of shared memory regions,
> interrupt registers, and status registers.
>
> The MCTP over PCC driver makes use of two PCC channels. For
> sending messages, it uses a Type 3 channel, and for receiving
> messages it uses the paired Type 4 channel. The device
> and corresponding channels are specified via ACPI.
>
> The first patch in the series implements a mechanism to allow the driver
> to indicate whether an ACK should be sent back to the caller
> after processing the interrupt. This is an optional feature in
> the PCC code, but has been made explicitly required in another driver.
> The implementation here maintains the backwards compatibility of that
> driver.
>
> The second patch in the series is the required change from ACPICA
> code that will be imported into the Linux kernel when synchronized
> with the ACPICA repository. It ahs already merged there and will
> be merged in as is. It is included here so that the patch series
> can run and be tested prior to that merge.

This cover letter looks woefully insufficient.

What is the end user visible effect of merging these patches, or not
merging these patches? I.e. what does Linux gain by merging them, what
pressing end user need goes unsatisfied if these are not merged? What is
the security model for these commands, i.e. how does a distro judge
whether this facility allows bypass of Kernel Lockdown protections?

The Kconfig does not help either. All this patch says is "communication
path exists, plumb it direct to userspace", with no discussion of
intended use cases, assumptions, or tradeoffs.