Plea for help with GPIO pin naming

[Supreeth Venkatesh]

On 8/26/24 15:46, Bills, Jason M wrote:
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>
> On 8/26/2024 12:35 PM, Johannes Truschnigg wrote:
>> Dear list,
>>
>> in my ongoing hobbyist quest to port OpenBMC to the Gigabyte 
>> MC12-LE0, I face
>> some challenges that leave me scratching my head - hence me posting 
>> here.
>> Today's questions concern GPIO line names and x86-power-control aka
>> /usr/bin/power-control.
>>
>> I've been reverse-engineering my board's GPIO pins for a while now, 
>> and once I
>> figure out what a particular pin is (probably) actually good and used 
>> for, I
>> most of the time have a hard time identifying the proper name/label 
>> for that
>> particular pin.
>>
>> I don't have a background in electronics, much less PCB design, but I 
>> guess
>> most line names in OpenBMC's DTS files are lifted verbatim from board
>> schematics, which I do not have for my board. That, as well as the 
>> sprawl of
>> pin labels and names used between existing platforms and boards, 
>> makes it very
>> hard for me to infer the meaning of most pins defined for supported 
>> OpenBMC
>> machines.
>
> The original thought in x86-power-control was for the GPIO names to
> remain static and be routed to the correct pin in the DTS. This didn't
> turn out to be the direction, so the config file was created later to
> allow specifying GPIO names.My research led me to a design document 
> from 2020 with the promising title
> "Device Tree GPIO Naming in OpenBMC"[0], but since I can't seem to 
> find the
> proposed names in any of OpenBMC meta layers, I guess it always 
> remained a
> proposal, without proper uptake in the real world? This hunch of mine is
> somewhat exacerbated by the fact that the x86-power-control package 
> assumes
> very different pin names in its default example config file[1] 
> (although a
> GitHub issue[2] exists that makes it somewhat plausible that might not 
> be 100%
> deliberate)...
>
> The GPIO names in x86-power-control pre-date the proposal and would just
> need some transition with backward-compatibility to move to the proposed
> names, if the community would like to go that direction.
>
> If I understand that GitHub issue, it's just that the README doesn't
> list all the GPIOs that must be defined (which doesn't really apply
> anymore since the config file allows any GPIO name). But it may be good
> to update the README overall.

>
>>
>> What I'd like to have is a solid guideline on how to interpret 
>> existing boards'
>> DTS pin names (unfortunately, I don't know what either of 
>> SIO_POWER_GOOD or
>> PS_PWROK exactly describe, or what the difference between the 
>> concepts the two
>> strings of characters map to in the physical world might be), 
>> assuming little
>> prior knowledge of these dark arts. Is there material on the web that 
>> isn't
>> buried under mountains of mainboard-designer-specific NDAs that could 
>> help me
>> with making sense of all the jargon I don't know? I'd be very 
>> thankful if
>> someone could point me a way!
>
> I won't be able to help with general guidelines for existing boards'
> DTSes, but I can definitely help with what x86-power-control uses.
>
> SIO_POWER_GOOD is named for the POWER_GOOD pin on the Aspeed BMC SIO
> signal block (probably a poor name in hindsight). On every system I have
> worked on, the CPU Power Good signal has been connected to that BMC pin.
> In x86-power-control, this signals that the system is fully powered and
> running.
>
> PS_PWROK is the Power Good or Power OK signal from the power supplies.
> In x86-power-control, this signals that the power supplies are enabled
> and supplying power to the system.
There was some effort to standardize the boot sequence by providing an 
example in open compute project DC-SCM specification.
Please refer to Section 3.5.15 Power States and Boot Sequence in 
https://www.opencompute.org/documents/ocp-dc-scm-2-0-ver-1-0-pdf
which may help decode plethora of pin names.
>
>>
>> Thanks very much for reading this far! :)
>>
>> [0]: 
>> https://github.com/openbmc/docs/blob/master/designs/device-tree-gpio-naming.md
>> [1]: 
>> https://github.com/openbmc/x86-power-control/blob/master/config/power-config-host0.json
>> [2]: https://github.com/openbmc/x86-power-control/issues/4
>>