Re: [PATCH v2 1/2] PCI: brcmstb: Add regulator support

[Florian Fainelli <f.fainelli@gmail.com>]

On 2/21/20 9:11 AM, Mark Brown wrote:
> On Fri, Feb 21, 2020 at 08:33:36AM -0800, Florian Fainelli wrote:
>> On 2/21/2020 4:12 AM, Mark Brown wrote:
> 
>>> No, this isn't a good idea - the set of supplies the device has is
>>> fixed when the silicon is produced, it's not something that needs to
>>> vary per board.  This means that the binding should have a fixed list of
>>> supplies, per SoC if that's needed.
> 
>> These are not the supplies for the PCIe I/Os on the SoCs side, but the
>> supplies for the PCIe end-point connected to the SoCs. More on that below.
> 
> Then the "slots" (obviously at least some of these are soldered down
> rather than on actual slots) should be represented in DT and the
> controller or bus should know that it needs to iterate over them to
> bring up the chips.  I would also expect that there are standard names
> in the PCI specs for the standard supplies that go into devices as part
> of the bus spec which would mean that there should still be no need to
> encode names like this.

Agree.

> 
>> If you describe the regulators as properties of the PCIe EP nodes which
>> are child nodes of the PCIe RC node (as we should), you will not be able
>> to manage all of them within your pci_driver instance, because if there
>> is no power to the EP you just do not enumerate it, therefore no
>> pci_device is created.
> 
> The framework and/or driver can enumerate firmware information without
> actually powering up the devices of course.

The issue is not enumeration, it is ensuring that you will be able to
establish the PCIe link with the EP. If there is no pci_device created
because the bus scanning returned a link down, there is not much that
can be done. Also the question is whether this logic belongs in the PCI
bus layer or the driver.

> 
> I would not be surprised to learn that most systems just mark the device
> supplies always on, it's not like the devices will be able to use them
> normally anyway.

In the downstream PCIe driver which is this one is just a subset of
until we close the gap, we have some additional logical to determine
whether the EP device is wakeup enabled in order to leave its regulators
turned on during system sleep so as to permit Wake-on-WLAN for instance.
-- 
Florian