Re: [Openipmi-developer] ipmi_si feature request: SMBIOS-based autoloading

From: Andy Lutomirski
Date: Tue Jan 26 2016 - 12:29:59 EST

On Tue, Jan 26, 2016 at 5:43 AM, Corey Minyard <minyard@xxxxxxx> wrote:
> On 01/26/2016 07:32 AM, Corey Minyard wrote:
>> On 01/24/2016 07:45 PM, Andy Lutomirski wrote:
>>> ipmi_si doesn't autoload on systems where it's found via SMBIOS.
>>> Could that be fixed?
>> I'm not really sure. I kind of assumed this was handled in userland
>> like the ACPI tables. I don't think there are many systems that have
>> SMBIOS and not ACPI, so I'm not sure of the impact here or what
>> to do.

I've never seen it handled in userland adequately on Fedora, Ubuntu, or CentOS.

FWIW, it might pay to have ipmi_si pull in ipmi_devintf as well. Then
ipmitool would work out of the box.

>>> If I were doing it, I'd suggest rigging up some code that's compiled
>>> in to the main kernel even if ipmi_si is a module that creates the
>>> platform device if the dmi device is there and then set up a modalias
>>> so that the platofrm device causes ipmi_si to load.
>>> (In general, having the same driver create the platform device and
>>> register the platform driver means that autoloading is unlikely to
>>> work right. See arch/x86/kernel/pmem.c for an example of a weird
>>> legacy device that gets this right.)
>> This sounds like kind of a hack.

It's a bit of a hack in that case. It does preserve the general
driver model approach where a lower-level thing enumerates the system
and instantiates devices and then a higher-level driver binds to the

>>> Alternatively, maybe /sys/firmware/dmi could learn how to advertise
>>> modaliases. But that might be a giant mess to solve a tiny problem.
>> This sounds like the right way, but you are probably right. Are
>> there any other resources that could benefit from this? I"m
>> guessing not.

No clue. Jean might know. Jean?

>> There is already a "dmi_save_ipmi_device" function that gets called
>> when scanning the SMBIOS table (see drivers/firmware/dmi_scan.c).
>> Maybe a tie-in there? That happens pretty early, though, I'm not
>> sure if it's too early.
>> Of course it would be easy to have a file like pmem.c that detects
>> if an IPMI device is in the SMBIOS table and create a platform
>> device for it.
>> Are you willing to do this work?

I'm willing to do some plumbing, but I'm not sure I want to dig deeply
into the innards of ipmi_si initialization.

>> -corey
> Actually, there is some cleanup that has to occur here, let me look at this
> a little bit.

It looks like the driver currently decides how to talk to the hardware
and then instantiates the platform device. For my approach to work,
it would have to be refactored a bit: instantiate the platform device
with the info about how to talk to hardware and then have the platform
driver fish that info back out of the platform device. Is that what
you're talking about?

I also don't understand the distinction between ipmi_si and ipmi_bmc.