linux-kernel - Re: [PATCH v3 2/4] dt-bindings: can: fixed-transceiver: Add new CAN fixed transceiver bindings

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Date:   Thu, 3 Aug 2017 10:38:29 -0500
From:   Franklin S Cooper Jr <fcooper@...com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-can@...r.kernel.org>,
        <wg@...ndegger.com>, <mkl@...gutronix.de>, <robh+dt@...nel.org>,
        <quentin.schulz@...e-electrons.com>,
        <dev.kurt@...dijck-laurijssen.be>, <andrew@...n.ch>,
        <socketcan@...tkopp.net>
Subject: Re: [PATCH v3 2/4] dt-bindings: can: fixed-transceiver: Add new CAN
 fixed transceiver bindings



On 08/03/2017 07:22 AM, Sergei Shtylyov wrote:
> On 08/03/2017 12:48 PM, Franklin S Cooper Jr wrote:
> 
>>>> Add documentation to describe usage of the new fixed transceiver
>>>> binding.
>>>> This new binding is applicable for any CAN device therefore it
>>>> exists as
>>>> its own document.
>>>>
>>>> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
>>>> ---
>>>>    .../bindings/net/can/fixed-transceiver.txt         | 24
>>>> ++++++++++++++++++++++
>>>>    1 file changed, 24 insertions(+)
>>>>    create mode 100644
>>>> Documentation/devicetree/bindings/net/can/fixed-transceiver.txt
>>>>
>>>> diff --git
>>>> a/Documentation/devicetree/bindings/net/can/fixed-transceiver.txt
>>>> b/Documentation/devicetree/bindings/net/can/fixed-transceiver.txt
>>>> new file mode 100644
>>>> index 0000000..2f58838b
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/net/can/fixed-transceiver.txt
>>>> @@ -0,0 +1,24 @@
>>>> +Fixed transceiver Device Tree binding
>>>> +------------------------------
>>>> +
>>>> +CAN transceiver typically limits the max speed in standard CAN and
>>>> CAN FD
>>>> +modes. Typically these limitations are static and the transceivers
>>>> themselves
>>>> +provide no way to detect this limitation at runtime. For this
>>>> situation,
>>>> +the "fixed-transceiver" node can be used.
>>>> +
>>>> +Required Properties:
>>>> + max-bitrate:    a positive non 0 value that determines the max
>>>> +        speed that CAN/CAN-FD can run. Any other value
>>>> +        will be ignored.
>>>> +
>>>> +Examples:
>>>> +
>>>> +Based on Texas Instrument's TCAN1042HGV CAN Transceiver
>>>> +
>>>> +m_can0 {
>>>> +    ....
>>>> +    fixed-transceiver@0 {
>>>
>>>     The <unit-address> (after @) must only be specified if there's "reg"
>>
>> Sorry. Fixed this in my v2 and some how it came back. Will fix.
>>
>>> prop in the device node. Also, please name the node "can-transceiver@"
>>> to be more in line with the DT spec. which requires generic node names.
>>
>> Its possible for future can transceivers drivers to be created. So I
> 
>    So what? Ah, you are using the node name to match in the CAN drivers...
> 
>> thought including fixed was important to indicate that this is a "dumb"
>> transceiver similar to "fixed-link".
> 
>    I'm not sure the "fixed-link" MAC subnode assumed any transceiver at
> all...

Your right. I wasn't trying to imply that it does. What I meant was that
having a node named "can-transceiver" may be a bit confusing in the
future if can transceiver drivers are created. Prefix of "fixed" atleast
to me makes it clear that this is something unique or a generic
transceiver with limitations. Similar to "fixed-link" which is for MACs
not connected to MDIO managed phy. Calling this subnode
"can-transceiver" to me would be like renaming "fixed-link" to "phy".

> 
>> So would "fixed-can-transceiver" be
>> ok or do you want to go with can-transceiver?
> 
>    I'm somewhat perplexed at this point...

If my reasoning still didn't change your views then I'll make the switch.
> 
> MBR, Sergei