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

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Message-ID: <191035b8c28.279b.9b12b7fc0a3841636cfb5e919b41b954@broadcom.com>
Date: Tue, 30 Jul 2024 13:16:57 +0200
From: Arend Van Spriel <arend.vanspriel@...adcom.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Jacobe Zang <jacobe.zang@...ion.com>, <robh@...nel.org>, <krzk+dt@...nel.org>, <heiko@...ech.de>, <kvalo@...nel.org>, <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>, <conor+dt@...nel.org>, Linus Walleij <linus.walleij@...aro.org>
CC: <efectn@...tonmail.com>, <dsimic@...jaro.org>, <jagan@...eble.ai>, <devicetree@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, <linux-rockchip@...ts.infradead.org>, <linux-kernel@...r.kernel.org>, <arend@...adcom.com>, <linux-wireless@...r.kernel.org>, <netdev@...r.kernel.org>, <megi@....cz>, <duoming@....edu.cn>, <bhelgaas@...gle.com>, <minipli@...ecurity.net>, <brcm80211@...ts.linux.dev>, <brcm80211-dev-list.pdl@...adcom.com>, <nick@...das.com>
Subject: Re: [PATCH v5 2/5] dt-bindings: net: wireless: brcm4329-fmac: add clock description for AP6275P

On July 30, 2024 12:18:20 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:

> On 30/07/2024 11:52, Arend Van Spriel wrote:
>> On July 30, 2024 11:01:43 AM Krzysztof Kozlowski <krzk@...nel.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@...ion.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@...adcom.com>
>>>>> Signed-off-by: Jacobe Zang <jacobe.zang@...ion.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.

Regards,
Arend

> Best regards,
> Krzysztof