SATA hotplug notifications for BMC inventory updates

[Paul Fertser]

Hello Johnathan,

Thank you for answering, please see inline.

On Tue, Sep 06, 2022 at 08:53:09AM -0700, Johnathan Mantey wrote:
> On 9/5/22 04:11, Paul Fertser wrote:
> 
>  Hi,
> 
>  An OCP Tioga Pass platform features up to 4 drive bays for SATA
>  storage accessible from the front and fully hot-pluggable. The
>  backplane is usually connected directly to Intel C620 PCH (aka
>  Lewisburg).
> 
>  It would be nice to have information about the currently attached
>  devices (model and serial number) available in BMC inventory but what
>  are the ways to get this information?
> 
> Intel systems only get drive mdl/sn from NVMe devices that provide that
> information via MCTP over SMBus. SAS/SATA drives, to my current knowledge, don't
> supply this info in that mode.

Indeed, NVMe provides this additional side-channel over SMBus
specifically for management, alas nothing like that is present in
SAS/SATA standards.

> The insertion/removal events are also managed from the BMC via I2C to a FPGA
> solution residing on the Hot Swap Backplane. The FPGA provides registers that
> allow the BMC to query the PRSTn/IFDETn pins.

I can also imagine I2C GPIO expanders doing the job, yes, this seems
to be reasonably straightforward.

>  Is it possible there's some additional module in the all-mighty ME
>  that can supply BMC with the current state of PCH SATA controller? Or
>  is there some other sensible mechanism other than talking to UEFI on
>  startup (which would mean BMC is showing stale and thus misleading
>  data till the next reboot)?
> 
>  Even though the question is quite specific we'd appreciate any related
>  insights on the topic; there must be some side-channels to RAID
>  controllers and such for BMC to be obtaining essential information but
>  so far I wasn't able to find any documentation about this.
> 
> RAID solutions are outside of scope for the Intel BMC.

Intel VROC too? Why? We'd be willing to contribute some development
effort into bringing RAID monitoring and management to OpenBMC,
wouldn't the community benefit from that? Many other vendors currently
offer this feature, why shouldn't OpenBMC? The problem seems to be
with the documentation availability; can you please tell where the
relevant hardware and protocols are described?

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