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

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Message-ID: <3d3b8e0a-7492-4db1-bd73-c30a488edaa7@kernel.org>
Date: Tue, 30 Jul 2024 12:18:06 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Arend Van Spriel <arend.vanspriel@...adcom.com>,
 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 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
about hardware - does this node, which represents PCI interface of the
chip, has/uses the clocks?

Best regards,
Krzysztof