linux-kernel - Re: [PATCH v3 4/5] wifi: brcmfmac: Add optional lpo clock enable support

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Message-ID:
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Date: Mon, 1 Jul 2024 10:57:36 +0000
From: Jacobe Zang <jacobe.zang@...ion.com>
To: Arend Van Spriel <arend.vanspriel@...adcom.com>, Stefan Wahren
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Subject: Re: [PATCH v3 4/5] wifi: brcmfmac: Add optional lpo clock enable
 support

>> Am 30.06.24 um 11:15 schrieb Chen-Yu Tsai:
>>> On Sun, Jun 30, 2024 at 5:10 PM Jacobe Zang <jacobe.zang@...ion.com> wrote:
>>>> Hi Stefan,
>>>>
>>>>>> WiFi modules often require 32kHz clock to function. Add support to
>>>>>> enable the clock to PCIe driver.
>>>>> the low power clock is independent from the host interface like PCIe. So
>>>>> the clock handling should move to the common code. Sorry, not i cannot
>>>>> give a good suggestion, what's the best place for this.
>>>> I think the clock is used by the PCIe device so enable it in this file.
>>>> Also I checked
>>>> use of clock which in spi[0] or sdio[0] device was enabled similarly to this.
>>>>
>>>> [0]
>>>> https://lore.kernel.org/all/20210806081229.721731-4-claudiu.beznea@microchip.com/
>>> You're looking at the wrong driver. For brcmfmac, the lpo clock is toggled
>>> by the MMC pwrseq code. And for the Bluetooth side (where it really matters)
>>> for UARTs, it is in drivers/bluetooth/hci_bcm.c. and documented in the
>>> binding Documentation/devicetree/bindings/net/broadcom-bluetooth.yaml

As ChenYu said, hci_bcm.c has handled for bt clock. But it seemed that clock has
never handled in brcmfmac wifi driver. So I wonder does everyone all enable the
clock in BT node not wifi?

>> Thanks for clarifying. So this change handles the PCIe case without
>> bluetooth. For USB the clock control doesn't make sense.
>>
>> Sorry for the noise
>
> So someone could end up with both wifi and bt LPO clock defined in DTS
> file. Not sure if that can be expressed and validated in device tree, but
> at the least there should be a fair warning in both binding files that
> there can be only one!
>
> The LPO clock matters to the chip. It is not specific to the BT part. The

I also think that it is necessary to handle the clock in wifi driver, though.

> clock is important for the power-up cycle. The timing difference WL_REG_ON
> and BT_REG_ON is expressed in LPO clock cycles.

---
Best Regards
Jacobe