Re: [PATCH v5 2/5] dt-bindings: net: wireless: brcm4329-fmac: add clock description for AP6275P

Sebastian Reichel
2024-07-31T13:54:53Z

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Hi,

On Wed, Jul 31, 2024 at 02:57:37PM GMT, Arend van Spriel wrote:
> On 7/30/2024 7:38 PM, Sebastian Reichel wrote:
> > Hi,
> >
> > On Tue, Jul 30, 2024 at 01:16:57PM GMT, Arend Van Spriel wrote:
> > > On July 30, 2024 12:18:20 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> > >
> > > > On 30/07/2024 11:52, Arend Van Spriel wrote:
> > > > > On July 30, 2024 11:01:43 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> > > > >
> > > > > > On 30/07/2024 08:37, Arend Van Spriel wrote:
> > > > > > > + Linus W
> > > > > > >
> > > > > > > On July 30, 2024 5:31:15 AM Jacobe Zang <jacobe.zang@wesion.com> wrote:
> > > > > > >
> > > > > > > > Not only AP6275P Wi-Fi device but also all Broadcom wireless devices allow
> > > > > > > > external low power clock input. In DTS the clock as an optional choice in
> > > > > > > > the absence of an internal clock.
> > > > > > > >
> > > > > > > > Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
> > > > > > > > Signed-off-by: Jacobe Zang <jacobe.zang@wesion.com>
> > > > > > > > ---
> > > > > > > > .../bindings/net/wireless/brcm,bcm4329-fmac.yaml | 8 ++++++++
> > > > > > > > 1 file changed, 8 insertions(+)
> > > > > > > >
> > > > > > > > diff --git
> > > > > > > > a/Documentation/devicetree/bindings/net/wireless/brcm,bcm4329-fmac.yaml
> > > > > > > > b/Documentation/devicetree/bindings/net/wireless/brcm,bcm4329-fmac.yaml
> > > > > > > > index 2c2093c77ec9a..a3607d55ef367 100644
> > > > > > > > --- a/Documentation/devicetree/bindings/net/wireless/brcm,bcm4329-fmac.yaml
> > > > > > > > +++ b/Documentation/devicetree/bindings/net/wireless/brcm,bcm4329-fmac.yaml
> > > > > > > > @@ -122,6 +122,14 @@ properties:
> > > > > > > > NVRAM. This would normally be filled in by the bootloader from platform
> > > > > > > > configuration data.
> > > > > > > >
> > > > > > > > + clocks:
> > > > > > > > + items:
> > > > > > > > + - description: External Low Power Clock input (32.768KHz)
> > > > > > > > +
> > > > > > > > + clock-names:
> > > > > > > > + items:
> > > > > > > > + - const: lpo
> > > > > > > > +
> > > > > > >
> > > > > > > We still have an issue that this clock input is also present in the
> > > > > > > bindings specification broadcom-bluetooth.yaml (not in bluetooth
> > > > > > > subfolder). This clock is actually a chip resource. What happens if both
> > > > > > > are defined and both wifi and bt drivers try to enable this clock? Can this
> > > > > > > be expressed in yaml or can we only put a textual warning in the property
> > > > > > > descriptions?
> > > > > >
> > > > > > Just like all clocks, what would happen? It will be enabled.
> > > > >
> > > > > Oh, wow! Cool stuff. But seriously is it not a problem to have two entities
> > > > > controlling one and the same clock? Is this use-case taken into account by
> > > > > the clock framework?
> > > >
> > > > Yes, it is handled correctly. That's a basic use-case, handled by CCF
> > > > since some years (~12?). Anyway, whatever OS is doing (or not doing)
> > > > with the clocks is independent of the bindings here. The question is
> > >
> > > Agree. Probably the bindings would not be the place to document this if it
> > > would be an issue.
> > >
> > > > about hardware - does this node, which represents PCI interface of the
> > > > chip, has/uses the clocks.
> > >
> > > The schematics I found for the wifi module and the khadas edge platform show
> > > these are indeed wired to the chip.
> >
> > I have a Rockchip RK3588 Evaluation Board on my desk, which uses the
> > same WLAN AP6275P module. I think I already commented on a prior
> > version of this series: The LPO clock is needed to make the PCIe
> > device visible on the bus. That means this series only works if the
> > clock has already been running. Otherwise the PCIe driver will never
> > be probed. To become visible the devices requires:
> >
> > 1. The LPO clock to be enabled
> > 2. Power to be applied
> > 3. The WL_EN gpio to be configured correctly
> >
> > If one of the above is not met, the device will not even appear in
> > 'lspci'. I believe the binding needs to take into consideration, that
> > pwrseq is needed for the PCIe side. Fortuantely the heavy lifting of
> > creating the proper infrastructure for this has already been done by
> > Bartosz Golaszewski for Qualcomm WLAN chips. What is missing is a
> > pwrseq driver for the Broadcom chip (or this specific module?).
>
> That does not really make sense. There is no relation between the LPO clock
> and the PCIe clocks so 1) being a requirement for probing the device looks
> odd. It also does not match past experience when I assisted Andy Green in
> getting this module up and running almost two years ago.

Well, first of all I can easily reproduce this on my RK3588 EVB1. I
intentionally ignore any bluetooth bits to avoid cross-effects from
bluetooth enabling any clocks / regulators / GPIOs and make sure the
RTC output clock is disabled at boot time (i.e. boot once without
any reference to the RTC clock and without 'clk_ignore_unused'
kernel argument). When booting up like this the WLAN device is not
visible in 'lspci' despite the WL_REG_ON GPIO being hogged. If I
additionally hack the RTC output clock to be enabled the WLAN device
becomes visible in 'lspci'.

The datasheet fully explains this:

https://www.lcsc.com/datasheet/lcsc_datasheet_2203281730_AMPAK-Tech-AP6275P_C2984107.pdf

PDF Page 23/24 (20/21 in the footer) has the Host Interface Timing
Diagram. WL_REG_ON should only be enabled after 2 cycles from LPO.
That means with LPO being disabled WL_REG_ON cannot be enabled. I'm
pretty sure WL_REG_ON means WLAN_REGULATOR_ON, so the logic is not
powered. On page 27 (24 in the footer) there is also a PCIe Power-On
Timing diagram, which shows that WL_REG_ON must be enabled before
the PCIe refclk is enabled.

So there is a specific power up sequence, which must be followed.

Greetings,

-- Sebastian

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