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
> > <[email protected]> wrote:
> > >
> > > On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <[email protected]>
> > > >
> > > > 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?
(I'm not questioning the need for having a bus, creating devices, and
matching/binding them to a set of drivers)
Regards,
Bjorn
> > Now as for the implementation, the way I see it we have two solutions:
> > either we introduce a fake, top-level PCI slot platform device device
> > that will reference the PCI host controller by phandle or we will live
> > with a secondary, "virtual" platform device for power sequencing that
> > is tied to the actual PCI device. The former requires us to add DT
> > bindings, add a totally fake DT node representing the "slot" which
> > doesn't really exist (and Krzysztof already expressed his negative
> > opinion of that) and then have code that will be more complex than it
> > needs to be. The latter allows us to not change DT at all (other than
> > adding regulators, clocks and GPIOs to already existing WLAN nodes),
> > reuse the existing parent-child relationship between the port node and
> > the instantiated platform device as well as result in simpler code.
> >
> > Given that DT needs to be stable while the underlying C code can
> > freely change if we find a better solution, I think that the second
> > option is a no-brainer here.
>
> Ok, I remove my objections, sorry about that, my confusion.
>
> greg k-h
On Wed, Jan 31, 2024 at 12:04:14PM +0100, Bartosz Golaszewski wrote:
> On Tue, Jan 30, 2024 at 10:54 PM Bjorn Andersson <[email protected]> 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
> > > > <[email protected]> wrote:
> > > > >
> > > > > On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
> > > > > > From: Bartosz Golaszewski <[email protected]>
> > > > > >
> > > > > > 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.
Said platform_device is also not a child under the PCIe bus, so this
would be a different platform_device...
> 2. The platform bus already provides us with the entire infrastructure
> that we'd now need to duplicate (possibly adding bugs) in order to
> introduce a "power sequencing bus".
>
This is a perfectly reasonable desire. Look at our PMICs, they are full
of platform_devices. But through the years it's been said many times,
that this is not a valid or good reason for using platform_devices, and
as a result we have e.g. auxiliary bus.
Anyway, (please) don't claim that "we need to", when it actually is "we
want to use platform_device because that's more convenient"!
Regards,
Bjorn
> Bart
>
> > (I'm not questioning the need for having a bus, creating devices, and
> > matching/binding them to a set of drivers)
> >
> > Regards,
> > Bjorn
> >
>
> [snip]
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 <[email protected]> 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
>>>>> <[email protected]> wrote:
>>>>>>
>>>>>> On Wed, Jan 17, 2024 at 05:07:43PM +0100, Bartosz Golaszewski wrote:
>>>>>>> From: Bartosz Golaszewski <[email protected]>
>>>>>>>
>>>>>>> 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
On Wed, Feb 07, 2024 at 05:32:38PM +0100, Bartosz Golaszewski wrote:
> On Fri, Feb 2, 2024 at 11:02 AM Bartosz Golaszewski <[email protected]> wrote:
> >
> > On Fri, Feb 2, 2024 at 1:03 AM Bjorn Andersson <[email protected]> wrote:
> > >
> >
> > [snip]
> >
> > > > >
> > > > > 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.
> > >
> >
> > My bad. In RB5 it isn't (yet - I want to add it in the power
> > sequencing series). It is in X13s though[1].
> >
> > > Said platform_device is also not a child under the PCIe bus, so this
> > > would be a different platform_device...
> > >
> >
> > It's the child of the PCIe port node but there's a reason for it to
> > have the `compatible` property. It's because it's an entity of whose
> > existence we are aware before the system boots.
> >
> > > > 2. The platform bus already provides us with the entire infrastructure
> > > > that we'd now need to duplicate (possibly adding bugs) in order to
> > > > introduce a "power sequencing bus".
> > > >
> > >
> > > This is a perfectly reasonable desire. Look at our PMICs, they are full
> > > of platform_devices. But through the years it's been said many times,
> > > that this is not a valid or good reason for using platform_devices, and
> > > as a result we have e.g. auxiliary bus.
> > >
> >
> > Ok, so I cannot find this information anywhere (nor any example). Do
> > you happen to know if the auxiliary bus offers any software node
> > integration so that the `compatible` property from DT can get
> > seamlessly mapped to auxiliary device IDs?
> >
>
> So I was just trying to port this to using the auxiliary bus, only to
> find myself literally reimplementing functions from
> drivers/of/device.c. I have a feeling that this is simply wrong. If
> we're instantiating devices well defined on the device-tree then IMO
> we *should* make them platform devices. Anything else and we'll be
> reimplementing drivers/of/ because we will need to parse the device
> nodes, check the compatible, match it against drivers etc. Things that
> are already implemented for the platform bus and of_* APIs.
>
> Greg: Could you chime in and confirm that it's alright to use the
> platform bus here? Or maybe there is some infrastructure to create
> auxiliary devices from software nodes?
Note, I HATE the use of the platform bus here, but I don't have a better
suggestion.
I'd love for the auxbus to work, and if you can create that from
software nodes, all the better! But I don't think that's possible just
yet, and you would end up implementing all the same stuff that the
platform bus has today for this functionality, so I doubt it would be
worth it.
thanks,
greg k-h