[PATCH v3 04/11] imx8mp: power-domain: Don't power off pd_bus

[Marek Vasut]

On 3/15/24 11:41 AM, Sumit Garg wrote:
> On Fri, 15 Mar 2024 at 14:53, Marek Vasut <marex at denx.de> wrote:
>>
>> On 3/15/24 6:31 AM, Sumit Garg wrote:
>>> On Thu, 14 Mar 2024 at 09:45, Marek Vasut <marex at denx.de> wrote:
>>>>
>>>> On 3/12/24 8:03 AM, Sumit Garg wrote:
>>>>> power_domain_on/off() isn't refcounted and power domain bus shouldn't be
>>>>> turned off for a single peripheral domain as it would negatively affect
>>>>> other peripheral domains. So lets just skip turning off bus power
>>>>> domain.
>>>>
>>>> What exactly is the issue and how did you trigger it ?
>>>>
>>>> Details please.
>>>
>>> I suppose the issue can be triggered via the "=> usb start => usb
>>> stop" sequence where one of the USB controllers is configured in
>>> peripheral mode.
>>
>> 'usb start ; usb stop' causes no problems on MX8MP , maybe the test case
>> is more extensive ?
>>
>> Please, write down the necessary steps to reproduce this problem, and
>> what happens when that problem occurs.
> 
> After digging in more, it looks like dev_power_domain_off() is never
> (U-Boot life-cycle) invoked for USB controller devices derived from
> DT. So this USB power domain sequence is never reachable.

The imx8mp_hsiomix_off() is never called on 'usb stop' command ?

But then why would the 'usb start ; usb stop' test break power domain 
state here ?

> BTW, dev_power_domain_on() is invoked when USB controller devices are
> added based on DT.

I would expect imx8mp_hsiomix_off() to be called either on 'usb stop' or 
just before Linux boots .

[...]

>>>> Why not add counter into imx8mp_hsiomix_priv structure in this driver ?
>>>
>>> Sure I can do that but do you think the current approach can have any
>>> side effects?
>>
>> Bus domain not getting cycled (which can leave it in some odd state),
>> and increased power consumption if the next stage doesn't turn the
>> domain off.
> 
> Given above, would you like me to drop power domain off path entirely
> here?

Can the series go in without this patch ?

> I think if people are concerned about power consumption then it
> should be implemented properly in U-Boot to remove all the DT based
> devices before passing on control to the next stage.

I would expect imx8mp_hsiomix_off() to be called either on 'usb stop' or 
just before Linux boots (esp. at that point), so if you do not power off 
the bus domain before booting Linux, you may hand over a device which 
was not fully power cycled.

And sorry for the delay, I was a bit busy.