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

[Arend van Spriel <arend.vanspriel@broadcom.com>]

On 7/31/2024 7:50 PM, Sebastian Reichel wrote:
> Hi,
> 
> On Wed, Jul 31, 2024 at 05:12:43PM GMT, Arend Van Spriel wrote:
>> On July 31, 2024 3:54:52 PM Sebastian Reichel
>> <sebastian.reichel@collabora.com> wrote:
>>> On Wed, Jul 31, 2024 at 02:57:37PM GMT, Arend van Spriel wrote:
>>>> On 7/30/2024 7:38 PM, Sebastian Reichel wrote:
>>>>> 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.
>>
>> The chip also has an (less accurate) internal LPO so the 32khz sleep clock
>> in the diagram does not have to be an external clock. Maybe Ampak
>> bootstrapped the chip to disable the internal clock. Dunno.
>>
>> What Andy needed back then to get firmware running was a change in the nvram
>> file to force using the internal LPO, but the device was already visible on
>> the PCIe bus.
> 
> mh, I just tested again and I can no longer reproduce the LPO
> requirement for PCIe detection. Maybe it was something else all
> along (I did most of my tests quite some time ago).
> Sorry for the noise.

Hi Sebastian,

Thanks for letting it know.

Regards,
Arend

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