linux-kernel - Re: [PATCH net-next v28 1/1] mctp pcc: Implement MCTP over PCC Transport

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Message-ID: <20250904-spiffy-earthworm-of-aptitude-c13fc8@sudeepholla>
Date: Thu, 4 Sep 2025 11:48:07 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Adam Young <admiyo@...amperecomputing.com>
Cc: Jeremy Kerr <jk@...econstruct.com.au>,
	Sudeep Holla <sudeep.holla@....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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Huisong Li <lihuisong@...wei.com>
Subject: Re: [PATCH net-next v28 1/1] mctp pcc: Implement MCTP over PCC
 Transport

Hi Adam,

On Thu, Sep 04, 2025 at 12:05:42AM -0400, Adam Young wrote:
> Implementation of network driver for
> Management Control Transport Protocol(MCTP)
> over Platform Communication Channel(PCC)
> 
> DMTF DSP:0292
> https://www.dmtf.org/sites/default/files/standards/documents/\
> DSP0292_1.0.0WIP50.pdf
> 
> MCTP devices are specified via ACPI by entries
> in DSDT/SDST and reference channels specified
> in the PCCT.  Messages are sent on a type 3 and
> received on a type 4 channel.  Communication with
> other devices use the PCC based doorbell mechanism;
> a shared memory segment with a corresponding
> interrupt and a memory register used to trigger
> remote interrupts.
> 
> This driver takes advantage of PCC mailbox buffer
> management. The data section of the struct sk_buff
> that contains the outgoing packet is sent to the mailbox,
> already properly formatted  as a PCC message.  The driver
> is also responsible for allocating a struct sk_buff that
> is then passed to the mailbox and used to record the
> data in the shared buffer. It maintains a list of both
> outging and incoming sk_buffs to match the data buffers
> 
> If the mailbox ring buffer is full, the driver stops the
> incoming packet queues until a message has been sent,
> freeing space in the ring buffer.
> 
> When the Type 3 channel outbox receives a txdone response
> interrupt, it consumes the outgoing sk_buff, allowing
> it to be freed.
> 

Sorry for not reviewing your mailbox changes in time, but I have
comments/concerns on the changes merged. I will respond on the original
thread with questions if I manage to find it, but it doesn't look good
at all to me. So I would want these changes to be on hold(not to be
merged at all).

-- 
Regards,
Sudeep