linux-kernel - Re: [PATCH v2 1/2] dt-bindings: net: broadcom-bluetooth: Add property for autobaud mode

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Message-ID: <e6e83743-1441-dc53-fd1f-cdfb9a24932a@linaro.org>
Date:   Mon, 30 May 2022 09:44:49 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Hakan Jansson <hakan.jansson@...ineon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: net: broadcom-bluetooth: Add property
 for autobaud mode

On 23/05/2022 11:21, Hakan Jansson wrote:
> Hi Krzysztof,
> 
> Thanks for responding.
> 
> On 5/22/2022 10:14 AM, Krzysztof Kozlowski wrote:
>>> Some devices (e.g. CYW5557x) require autobaud mode to enable FW loading.
>> Which devices support this? You probably need allOf:if:then.
> 
> Most devices _support_ autobaud mode but I don't have a definitive list. 
> The CYW5557x is the first device family to _require_ autobaud mode for 
> FW loading as far as I know.
> 
>>> Autobaud mode can also be required on some boards where the controller
>>> device is using a non-standard baud rate when first powered on.
>>>
>>> This patch adds a property, "brcm,uses-autobaud-mode", to enable autobaud
>>> mode selection.
>> Don't use "This patch":
>> https://elixir.bootlin.com/linux/v5.17.1/source/Documentation/process/submitting-patches.rst#L95
> 
> Sorry, will change in next rev.
> 
>>> Signed-off-by: Hakan Jansson <hakan.jansson@...ineon.com>
>>> ---
>>> V1 -> V2: Modify property description
>>>
>>>   .../devicetree/bindings/net/broadcom-bluetooth.yaml      | 9 +++++++++
>>>   1 file changed, 9 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/broadcom-bluetooth.yaml b/Documentation/devicetree/bindings/net/broadcom-bluetooth.yaml
>>> index 5aac094fd217..a29f059c21cc 100644
>>> --- a/Documentation/devicetree/bindings/net/broadcom-bluetooth.yaml
>>> +++ b/Documentation/devicetree/bindings/net/broadcom-bluetooth.yaml
>>> @@ -92,6 +92,15 @@ properties:
>>>          pcm-sync-mode: slave, master
>>>          pcm-clock-mode: slave, master
>>>
>>> +  brcm,uses-autobaud-mode:
>> Based on description, I understand the host triggers using autobaud.
> 
> Correct, the host triggers using autobaud.
> 
>> However here you word it as "uses", so it is independent of host, it
>> looks like property of a device.
> 
> I've been thinking of it as a a property of a specific board HW, 
> inherited either from a property of the device being used or from a 
> property of the HW design (e.g. a PCB using an alternate crystal 
> frequency yielding a non-standard baud rate).
> 
>>   The commit msg describes it even
>> different - "require autobaud".
> 
> Yes, the commit message describes two separate reasons why autobaud mode 
> would be required:
> 
> 1. Requirement coming from Device: "Some devices (e.g. CYW5557x) require 
> autobaud mode to enable FW loading."
> 
> 2. Requirement coming from HW design: "Autobaud mode can also be 
> required on some boards where the controller device is using a 
> non-standard baud rate when first powered on."
> 
>> This leads to second issue - it looks like there is some hardware
>> property (requiring to use autobaud) which should be described by
>> bindings. But instead you describe desired operational feature.
> 
> Sorry about that. I've really been struggling with what should go into 
> the description. Any suggestions or hints would be much appreciated.
> 
> How about, changing the property name to "brcm,requires-autobaud-mode" 
> and the description to:
> "Set this property if autobaud mode is required. Autobaud mode is 
> required if the device's baud rate in normal mode is not supported by 
> the host or if the device requires autobaud mode startup before loading FW."
> 
> Would that be an appropriate name and description?

Yes, sounds good. I also have trouble to name it nicely.

Sorry for late reply.

Best regards,
Krzysztof