linux-kernel - Re: [PATCH 1/2] dt-bindings: net: bluetooth: nxp: add support for supply and reset

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Message-ID: <20241021102558.rfnz7nxcg5knibxs@pengutronix.de>
Date: Mon, 21 Oct 2024 12:25:58 +0200
From: Marco Felsch <m.felsch@...gutronix.de>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>,
	Sherry Sun <sherry.sun@....com>,
	Amitkumar Karwar <amitkumar.karwar@....com>,
	Neeraj Sanjay Kale <neeraj.sanjaykale@....com>,
	"marcel@...tmann.org" <marcel@...tmann.org>,
	"luiz.dentz@...il.com" <luiz.dentz@...il.com>,
	"robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	GEO-CHHER-bsp-development <bsp-development.geo@...ca-geosystems.com>
Subject: Re: [PATCH 1/2] dt-bindings: net: bluetooth: nxp: add support for
 supply and reset

On 24-10-21, Krzysztof Kozlowski wrote:
> On 21/10/2024 08:41, Marco Felsch wrote:
> > On 24-10-07, Krzysztof Kozlowski wrote:
> >> On 07/10/2024 14:58, POPESCU Catalin wrote:
> >>>>>>
> >>>>>> +  vcc-supply:
> >>>>>> +    description:
> >>>>>> +      phandle of the regulator that provides the supply voltage.
> >>>>>> +
> >>>>>> +  reset-gpios:
> >>>>>> +    description:
> >>>>>> +      Chip powerdown/reset signal (PDn).
> >>>>>> +
> >>>>> Hi Catalin,
> >>>>>
> >>>>> For NXP WIFI/BT chip, WIFI and BT share the one PDn pin, which means that both wifi and BT controller will be powered on and off at the same time.
> >>>>> Taking the M.2 NXP WIFI/BT module as an example, pin56(W_DISABLE1) is connected to the WIFI/BT chip PDn pin, we has already controlled this pin in the corresponding PCIe/SDIO controller dts nodes.
> >>>>> It is not clear to me what exactly pins for vcc-supply and reset-gpios you describing here. Can you help understand the corresponding pins on M.2 interface as an example? Thanks.
> >>>
> >>> Hi Sherry,
> >>>
> >>> Regulators and reset controls being refcounted, we can then implement 
> >>> powerup sequence in both bluetooth/wlan drivers and have the drivers 
> >>> operate independently. This way bluetooth driver would has no dependance 
> >>> on the wlan driver for :
> >>>
> >>> - its power supply
> >>>
> >>> - its reset pin (PDn)
> >>>
> >>> - its firmware (being downloaded as part of the combo firmware)
> >>>
> >>> For the wlan driver we use mmc power sequence to drive the chip reset 
> >>> pin and there's another patchset that adds support for reset control 
> >>> into the mmc pwrseq simple driver.
> >>>
> >>>> Please wrap your replies.
> >>>>
> >>>> It seems you need power sequencing just like Bartosz did for Qualcomm WCN.
> >>>
> >>> Hi Krzysztof,
> >>>
> >>> I'm not familiar with power sequencing, but looks like way more 
> >>> complicated than reset controls. So, why power sequencing is recommended 
> >>> here ? Is it b/c a supply is involved ?
> >>
> >> Based on earlier message:
> >>
> >> "For NXP WIFI/BT chip, WIFI and BT share the one PDn pin, which means
> >> that both wifi and BT controller will be powered on and off at the same
> >> time."
> >>
> >> but maybe that's not needed. No clue, I don't know the hardware. But be
> >> carefully what you write in the bindings, because then it will be ABI.
> > 
> > We noticed the new power-sequencing infrastructure which is part of 6.11
> > too but I don't think that this patch is wrong. The DT ABI won't break
> > if we switch to the power-sequencing later on since the "reset-gpios"
> > are not marked as required. So it is up to the driver to handle it
> > either via a separate power-sequence driver or via "power-supply" and
> > "reset-gpios" directly.
> 
> That's not the point. We expect correct hardware description. If you say
> now it has "reset-gpios" but later say "actually no, because it has
> PMU", I respond: no. Describe the hardware, not current Linux.

I know that DT abstracts the HW. That said I don't see the problem with
this patch. The HW is abstracted just fine:

shared PDn          -> reset-gpios
shared power-supply -> vcc-supply

Right now the DT ABI for the BT part is incomplete since it assume a
running WLAN part or some hog-gpios to pull the device out-of-reset
which is addressed by this patchset.

Making use of the new power-sequencing fw is a Linux detail and I don't
see why the DT can't be extended later on. We always extend the DT if
something is missing or if we found a better way to handle devices.

Regards,
  Marco