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

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Message-ID: <59df0d38-82f5-42af-af93-4cdf33fa89e7@amperemail.onmicrosoft.com>
Date: Thu, 4 Sep 2025 12:54:12 -0400
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: Sudeep Holla <sudeep.holla@....com>,
 Adam Young <admiyo@...amperecomputing.com>
Cc: Jeremy Kerr <jk@...econstruct.com.au>,
 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

On 9/4/25 06:48, Sudeep Holla wrote:
> 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).

Yeah, I was a little concerned those got merged without your input.  I 
will look for the comments.