Re: [PATCH 4/9] PCI: create platform devices for child OF nodes of the port node

[Jeff Johnson <quic_jjohnson@quicinc.com>]

On 2/1/2024 4:03 PM, Bjorn Andersson wrote:
> On Wed, Jan 31, 2024 at 12:04:14PM +0100, Bartosz Golaszewski wrote:
>> On Tue, Jan 30, 2024 at 10:54 PM Bjorn Andersson <andersson@kernel.org> wrote:
>>>
>>> On Thu, Jan 18, 2024 at 12:15:27PM +0100, Greg Kroah-Hartman wrote:
>>>> On Thu, Jan 18, 2024 at 11:58:50AM +0100, Bartosz Golaszewski wrote:
>>>>> On Wed, Jan 17, 2024 at 5:45 PM Greg Kroah-Hartman
>>>>> <gregkh@linuxfoundation.org> wrote:
>>>>>>
>>>>>> On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
>>>>>>> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>>>>>>>
>>>>>>> In order to introduce PCI power-sequencing, we need to create platform
>>>>>>> devices for child nodes of the port node.
>>>>>>
>>>>>> Ick, why a platform device?  What is the parent of this device, a PCI
>>>>>> device?  If so, then this can't be a platform device, as that's not what
>>>>>> it is, it's something else so make it a device of that type,.
>>>>>>
>>>>>
>>>>> Greg,
>>>>>
>>>>> This is literally what we agreed on at LPC. In fact: during one of the
>>>>> hall track discussions I said that you typically NAK any attempts at
>>>>> using the platform bus for "fake" devices but you responded that this
>>>>> is what the USB on-board HUB does and while it's not pretty, this is
>>>>> what we need to do.
>>>>
>>>> Ah, you need to remind me of these things, this changelog was pretty
>>>> sparse :)
>>>>
>>>
>>> I believe I missed this part of the discussion, why does this need to be
>>> a platform_device? What does the platform_bus bring that can't be
>>> provided by some other bus?
>>>
>>
>> Does it need to be a platform_device? No, of course not. Does it make
>> sense for it to be one? Yes, for two reasons:
>>
>> 1. The ATH11K WLAN module is represented on the device tree like a
>> platform device, we know it's always there and it consumes regulators
>> from another platform device. The fact it uses PCIe doesn't change the
>> fact that it is logically a platform device.
> 
> Are you referring to the ath11k SNOC (firmware running on co-processor
> in the SoC) variant?
> 
> Afaict the PCIe-attached ath11k is not represented as a platform_device
> in DeviceTree.

Are you considering out-of-tree drivers? My understanding is that there
are different PCIe modules, ones that don't have GPIO-control for x86
and ones that do have GPIO-control for ARM. The out-of-tree cnss
platform driver used for Android has a large amount of DT control
<https://git.codelinaro.org/clo/la/platform/vendor/qcom-opensource/wlan/platform/-/blob/wlan-platform.lnx.1.0.r1-rel/cnss2/power.c?ref_type=heads>

(not sure off hand where the DT files themselves are)

/jeff