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

From: Arend van Spriel
Date: Wed Jul 31 2024 - 09:01:24 EST


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@xxxxxxxxxx> wrote:

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

"""
On 11/9/22 18:26, Arend Van Spriel wrote:
> On November 8, 2022 11:48:22 AM Andy Green <andy@xxxxxxxxxxx> wrote:
>> Hi -
>>
>> I'm trying to bring up AP6275 support on 6.1-rc4... I have tried a forward-ported sdk broadcom driver from the 5.10 based soc sdk, and the mainline brcm fullmac driver.
>
> Do you have a reference to the SDK? For what SoC?

Hi Arend -

It's the OOT broadcom driver that came with the latest (Sept 2022) vendor SDK for RK3588, from Rockchip. Their evb has an AP6275 onboard.

PCIe generally is working on this (eg, for NVMe in the PCIe 4-lane slot) and for network, and the PCIe part seems OK when I hack in a gpio regulator to hold up the module enable gpio.
"""

So regarding 2) and 3) I agree with you.

Regards,
Arend