linux-kernel - Re: [PATCH] ipmi:ssif: Exit early when there is a SMBus error

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Message-ID: <84eb700ee647cc40e9e99b086a8648e3@suse.de>
Date: Sun, 18 Aug 2024 12:27:27 +0300
From: "Ivan T. Ivanov" <iivanov@...e.de>
To: corey@...yard.net
Cc: minyard@....org, openipmi-developer@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipmi:ssif: Exit early when there is a SMBus error

Hi,

On 2024-08-16 21:04, Corey Minyard wrote:
> On Fri, Aug 16, 2024 at 09:54:58AM +0300, Ivan T. Ivanov wrote:
>> It is pointless to continue module probing when communication
>> with device is failing. This just fill logs with misleading
>> messages like this:
> 
> So the BMC (or whatever is there) responds to a GET_DEVICE_ID command,

Well, not really. In cases where ssif_detect() returns -ENODEV, i2c core
i2c_detect_address() threat it as "We catch it here as this isn't an 
error”.
See i2c_detect_address().

> but then doesn't properly handle any other valid and mandatory 
> commands?
> And this device was added via ACPI or SMBIOS or device tree, almost
> certainly.
> 
> My comments are:
> 
> 1) This fix is wrong, because it may mask important things that need to
> be reported.
> 
> 2) Fix the source of the problem.  You can't expect software to
> compensate for all bad hardware and firmware.  I'd guess the firmware
> tables are pointing to something that's not a BMC.

I am not saying that hardware or firmware do not have its issues in this
case. But just as it is written now ssif_probe() is fragile. It continue
asking device for features ignoring that there is no valid SMBus 
communication.

> 
> 3) It appears the response to the GET_DEVICE_ID command, though a
> response is returned, is not valid.  The right way to handle this would
> be to do more validation in the ssif_detect() function.  It doesn't do
> any validation of the response data, and that's really what needs to be
> done.
> 

do_cmd() in ssif_detect() already do validation. Perhaps,
ssif_probe() should just not return ENODEV in case of error.

Thank you for your comments!

Regards,
Ivan