Re: [PATCH net-next v2] dt-bindings: net: ath11k: document the inputs of the ath11k on WCN6855

[Bartosz Golaszewski]

On Fri, Sep 6, 2024 at 8:38 PM Jeff Johnson <quic_jjohnson@xxxxxxxxxxx> wrote:
>
> On 9/6/2024 12:44 AM, Bartosz Golaszewski wrote:
> > For upstream - if you're using the WCN6855, you must specify the
> > inputs for the WLAN module so it's only fair they be described as
> > "required". For out-of-tree DTS I couldn't care less.
> >
> > You are not correct saying that "M.2 boards don't need these" because
> > as a matter of fact: the WLAN module on your M.2 card takes these
> > inputs from the PMU inside the WCN6855 package.
>
> Let me start by saying that DT is one area where I'm a newbie, so I hope I can
> get some education.
>
> I'd like to start with an observation: I've used both WCN6855 with ath11k and
> WCN7850 with ath12k on an x86 laptop without any device tree, so from that
> perspective none of the device tree stuff is "required" -- these modules "just
> work".
>

Yes. This is what I refer to as "fully dynamic" M.2 cards, where the
card typically has an on-board PMIC that handles the power-up of the
device, respecting all timings etc. No custom pins are used. You don't
need device-tree. DT bindings don't concern this case. Even it this
was an ARM, DT-based platform, you wouldn't need the DT entry.

> However I also realize that when these are installed on Qualcomm ARM platforms
> that there are GPIO pins that control things like XO clock, WLAN enable &
> Bluetooth enable, as well as voltage regulators, and the device is
> non-functional without those configured, so the device tree items are required
> in that environment.
>
> So just from that perspective saying something is "required" is confusing when
> there are platforms where it isn't required. And perhaps that is what is
> confusing Kalle as well?
>

The properties are required IF you have a DT representation. Because
if you're modeling the physical package, this is what it looks like.
The one on your "fully dynamic" M.2 card is the same - it also has the
same internal inputs and outputs but you're not modeling the external
package in the first place so you don't need to care about them. But
if you do represent the chipset and not as a black box WCN6855 in its
entirety but its WLAN, BT and PMU modules separately then it warrants
making the true inputs of the WLAN module mandatory in the schema.

Please let me know if this is enough of an explanation.

Bart