linux-kernel - Re: [PATCH v2 0/3] Add Aspeed SSIF BMC driver

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Message-ID: <0e7fceff-4a01-5cb0-72eb-8b47d598f1c3@os.amperecomputing.com>
Date:   Wed, 7 Apr 2021 20:09:50 +0700
From:   Quan Nguyen <quan@...amperecomputing.com>
To:     minyard@....org
Cc:     Rob Herring <robh+dt@...nel.org>, Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Wolfram Sang <wsa@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        openipmi-developer@...ts.sourceforge.net,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, openbmc@...ts.ozlabs.org,
        Open Source Submission <patches@...erecomputing.com>,
        Phong Vo <phong@...amperecomputing.com>,
        "Thang Q . Nguyen" <thang@...amperecomputing.com>
Subject: Re: [PATCH v2 0/3] Add Aspeed SSIF BMC driver

Hi Corey,

Thank you for reviewing
I'll put my respond inline below.

-Quan

On 02/04/2021 21:21, Corey Minyard wrote:
> On Tue, Mar 30, 2021 at 09:10:26PM +0700, Quan Nguyen wrote:
>> This series add support for the Aspeed specific SSIF BMC driver which
>> is to perform in-band IPMI communication with the host in management
>> (BMC) side.
> 
> I don't have any specific feedback for this, but I'm wondering if it's
> really necessary.
> 
> Why can't the BMC just open the I2C device and use it?  Is there any
> functionality that this provides that cannot be accomplished from
> userland access to the I2C device?  I don't see any.
>
> If it tied into some existing framework to give abstract access to a BMC
> slave side interface, I'd be ok with this.  But I don't see that.
> 

The SSIF at the BMC side acts as an I2C slave and we think that the 
kernel driver is unavoidable to handle the I2c slave events 
(https://www.kernel.org/doc/html/latest/i2c/slave-interface.html)

And to make it works with existing OpenBMC IPMI stack, a userspace part, 
ssifbridge, is needed (https://github.com/openbmc/ssifbridge). This 
ssifbridge is to connect this driver with the OpenBMC IPMI stack so the 
IPMI stack can communicate via SSIF channel in similar way that was 
implemented with BT and KCS (ie: btbridge/kcsbridge and its corespondent 
kernel drivers (https://github.com/openbmc/btbridge and 
https://github.com/openbmc/kcsbridge))

> Unless there is a big need to have this in the kernel, I'm against
> including this and would suggest you do all this work in userland.
> Perhaps write a library.  Sorry, but I'm trying to do my part to reduce
> unnecessary things in the kernel.
> 
> Thanks,
> 
> -corey
>