Question on States monitoring

[Lei YU]

Hi Andres,

The existing [phosphor-gpio-monitor][1] contains two services, one is for
monitor gpio interrupts, the other is "phosphor-gpio-presence" that checks a
gpio output and let it be some state on DBus.

I guess the "presence" service is what you are looking for, that maps a
gpio output to a Dbus object.

The existing use case is:
1. Witherspoon checks if power supply is connected and create dbus object
   /inventory/system/chassis/motherboard/powersupplyX, it also is able to
   bind the kernel driver when it is attached.
2. Zaius checks if a PCIE card is connected on E2B and create dbus object
   /inventory/system/chassis/pcie_card_e2b

You can see a little detailed explanation at
https://github.com/mine260309/openbmc-intro/blob/master/Porting_Guide.md#gpio-presence

[1]: https://github.com/openbmc/phosphor-gpio-monitor

On Tue, May 15, 2018 at 7:26 AM, Andres Oportus
<andresoportus at google.com> wrote:
> Thanks Andrew, yeah I see the design philosophy of not exposing low level
> stuff like GPIOs unless they mean something more high level (hence the
> "State" reference) that could be exposed/monitored/changed/etc.  I'm just
> checking to see if we have anything already being thought of or implemented
> as to not come up with a custom solution.  The problem is managing "States"
> at least initially backed by GPIOs, and it does not have to be on the DBUS
> although from what I've seen for instance on IPMI we use DBUS extensively
> for things that get exported.
>
> On Mon, May 14, 2018 at 4:16 PM Andrew Jeffery <andrew at aj.id.au> wrote:
>>
>> Hi Andres,
>>
>> On Tue, 15 May 2018, at 01:16, Andres Oportus wrote:
>> > Are there any ongoing efforts on expanding States (say provided by
>> > GPIOs)
>> > monitoring/management?  I see that phosphor-state-manager has
>> > Chassis/Host/BMC states that are placed onto DBUS but not a more generic
>> > mechanism.  On the GPIO specific side, I see that phosphor-gpio-monitor
>> > allows for interrupt driven GPIO monitoring (seemly only used under a
>> > gpio-keys driver with /dev/input for Power's checkstop monitoring?), but
>> > no
>> > generic GPIO setting/getting for those not allowing interrupt type
>> > monitoring (say output GPIOs).
>>
>> It's not clear to me what you're looking for here. Are you hoping for
>> something to expose the GPIOs on DBus? I don't think we have anything like
>> that, which is more of a design philosophy thing (we should probably provide
>> a higher-level capability on DBus, not just directly expose GPIOs).
>>
>> Alternatively if you're looking to handle GPIOs from your application, I
>> would recommend libgpiod:
>>
>> https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/
>>
>> Cheers,
>>
>> Andrew