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Date:   Tue, 30 Apr 2019 21:24:29 +0000
From:   Vadim Pasternak <vadimp@...lanox.com>
To:     Asmaa Mnebhi <Asmaa@...lanox.com>,
        "minyard@....org" <minyard@....org>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        Michael Shych <michaelsh@...lanox.com>
CC:     Asmaa Mnebhi <Asmaa@...lanox.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH v4 0/1] Add support for IPMB driver



> -----Original Message-----
> From: Asmaa Mnebhi <Asmaa@...lanox.com>
> Sent: Tuesday, April 30, 2019 8:59 PM
> To: minyard@....org; wsa@...-dreams.de; Vadim Pasternak
> <vadimp@...lanox.com>; Michael Shych <michaelsh@...lanox.com>
> Cc: Asmaa Mnebhi <Asmaa@...lanox.com>; linux-kernel@...r.kernel.org;
> linux-i2c@...r.kernel.org
> Subject: [PATCH v4 0/1] Add support for IPMB driver
> 
> Thank you for your feedback Vadim. I have addressed your comments.

Hi Asmaa,

Thank you for your comments and added doc.

> 
> 1) You are correct. This driver is not specific to Mellanox so I have removed the
> Mellanox attribute.
> 
> 2) I have added a documentation file called IPMB.txt which explains how this
> module works and how it should be instantiated. It is very similar to the existing
> linux i2c-slave-eeprom module.
> 
> The HW for my testing works as follows:
> A BMC is connected to a Satellite MC via I2C (I2C is equivalent to IPMB). The
> BMC initiates the IPMB requests and sends them via I2C.
> Obviously the BMC needs its own driver to do this which I haven't included in this
> code. We have no intent of upstreaming that at the moment.

I believe you are going to do it at some point, right?

> This ipmb-dev-int driver is to be loaded and instantiated on the Satellite MC to
> be able to receive IPMB requests. These IPMB request messages will be picked
> up by a user space program such (in my case it is OpenIPMI) to handle the
> request and generate a response.
> The response will be then passed from the user program back to kernel space.
> Then this driver would send that response back to the BMC.
> 
> 3) You asked the following:
> 
> "Is it expected to be zero in vaid case?"
> The 8 least significant bits of the sum is always expected to be 0 in the case
> where the checksum is valid. I have added a comment for clarifications.


> 
> "why do you need this cast?"
> buf[++ipmb_dev_p->msg_idx]=(u8)(client->addr<<1)
> This is because client->addr is of type unsigned short which is
> 2 bytes so it is safer to typecast it to u8 (u8* buf)

Better, if you can avoid cast.
Would compiler warn if you use for example
rol16(client->addr, 1) & GENMASK(7, 0);
or something like it?


> 
> "It could be only single ipmb-dev within the system? Couldn't it be few, like
> master/slave for example?"
> My understanding of your question is that: what if we have multiple instances of
> ipmb-dev-int, that we register it under different addresses?
> This driver only works as a slave so it will only be instantiated once on the
> Satellite MC under one slave address.

I mentioned some config like:
BMC1 (master)  -- busA --|
			Satellite
BMC2 (standby)	-- busB --| 

Since this is not Mellanox specific driver, maybe it would be good to support
multiple instances of it.

> 
> Asmaa Mnebhi (1):
>   Add support for IPMB driver
> 
>  Documentation/IPMB.txt           |  53 ++++++
>  drivers/char/ipmi/Kconfig        |   8 +
>  drivers/char/ipmi/Makefile       |   1 +
>  drivers/char/ipmi/ipmb_dev_int.c | 381
> +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 443 insertions(+)
>  create mode 100644 Documentation/IPMB.txt  create mode 100644
> drivers/char/ipmi/ipmb_dev_int.c
> 
> --
> 2.1.2

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