Re: [PATCH v3 0/4] regulator_sync_state() support

[Saravana Kannan]

On Wed, Jul 15, 2020 at 9:20 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
>
> Consider the following example:
> - regulator-X is provided by device-X.
> - regulator-X is a supplier to device-A, device-B and device-C.
> - device-A is off/inactive from boot.
> - device-B and device-C are left on/active by the bootloader
> - regulator-X is left on boot by the bootloader at 2000 mV to supply
>   device-B and device-C.
>
> Example boot sequence 1:
> 1. device-X is probed successfully.
> 2. device-A is probed by driver-A
>    a. driver-A gets regulator-X
>    b. driver-A votes on regulator-X
>    c. driver-A initializes device-A
>    d. driver-A votes off regulator-X
>    e. regulator-X is turned off.
> 3. System crashes or device-B and device-C become unreliable because
>    regulator-X was turned off without following the proper quiescing
>    steps for device-B and device-C.
>
> Example boot sequence 2:
> 1. device-X is probed successfully.
> 2. device-B is probed by driver-B
>    a. driver-B gets regulator-X
>    b. driver-B votes on regulator-X
>    c. driver-B lowers device-B performance point.
>    d. driver-B lowers voltage vote to 1000 mV.
>    e. regulator-X voltage is lowered to 1000 mV.
> 3. System crashes or device-C becomes unreliable because regulator-X
>    voltage was lowered to 1000 mV when device-C still needed it at 2000 mV

Marek,

I'd appreciate it if you could test this series to see if it fixes
your coupled regulator issue that you reported earlier. I'm expecting
it to fix it without needing any special case handling in your
regulator drivers. But it'll be good to get confirmation from you.

Thanks,
Saravana