linux-kernel - Re: [PATCH 1/4] dt-bindings: phy: Add binding for TI TCAN104x CAN transceivers

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Message-ID: <9350f367-2c4f-1779-ec24-94066e152992@ti.com>
Date:   Wed, 14 Apr 2021 18:23:19 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Rob Herring <robh@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>
CC:     Vignesh Raghavendra <vigneshr@...com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lokesh Vutla <lokeshvutla@...com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, <linux-can@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH 1/4] dt-bindings: phy: Add binding for TI TCAN104x CAN
 transceivers

Hi Marc,

On 13/04/21 6:45 pm, Rob Herring wrote:
> On Tue, Apr 13, 2021 at 2:41 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>>
>> On 12.04.2021 12:49:56, Rob Herring wrote:
>>> On Mon, Apr 12, 2021 at 12:19:30PM +0200, Marc Kleine-Budde wrote:
>>>> On 4/9/21 3:40 PM, Aswath Govindraju wrote:
>>>>> Add binding documentation for TI TCAN104x CAN transceivers.
>>>>>
>>>>> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
>>>>> ---
>>>>>  .../bindings/phy/ti,tcan104x-can.yaml         | 56 +++++++++++++++++++
>>>>>  1 file changed, 56 insertions(+)
>>>>>  create mode 100644 Documentation/devicetree/bindings/phy/ti,tcan104x-can.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/phy/ti,tcan104x-can.yaml b/Documentation/devicetree/bindings/phy/ti,tcan104x-can.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..4abfc30a97d0
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/phy/ti,tcan104x-can.yaml
>>>>> @@ -0,0 +1,56 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: "http://devicetree.org/schemas/phy/ti,tcan104x-can.yaml#"
>>>>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>>>>> +
>>>>> +title: TCAN104x CAN TRANSCEIVER PHY
>>>>> +
>>>>> +maintainers:
>>>>> +  - Aswath Govindraju <a-govindraju@...com>
>>>>> +
>>>>> +properties:
>>>>> +  $nodename:
>>>>> +    pattern: "^tcan104x-phy"
>>>>> +
>>>>> +  compatible:
>>>>> +    enum:
>>>>> +      - ti,tcan1042
>>>>> +      - ti,tcan1043
>>>>
>>>> Can you create a generic standby only and a generic standby and enable transceiver?
>>>
>>> As a fallback compatible fine, but no generic binding please. A generic
>>> binding can't describe any timing requirements between the 2 GPIO as
>>> well as supplies when someone wants to add those (and they will).
>>
>> Right - that makes sense.
>>

So, I need not add any new compatible strings right because as a
fallback the existing compatible strings can be used, as there are no
timing constraints on them.

Thanks,
Aswath

>>>>> +
>>>>> +  '#phy-cells':
>>>>> +    const: 0
>>>>> +
>>>>> +  standby-gpios:
>>>>> +    description:
>>>>> +      gpio node to toggle standby signal on transceiver
>>>>> +    maxItems: 1
>>>>> +
>>>>> +  enable-gpios:
>>>>> +    description:
>>>>> +      gpio node to toggle enable signal on transceiver
>>>>> +    maxItems: 1
>>>>> +
>>>>> +  max-bitrate:
>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>> +    description:
>>>>> +      max bit rate supported in bps
>>>
>>> We already have 'max-speed' for serial devices, use that.
>>
>> There is already the neither Ethernet PHY (PHYLINK/PHYLIB) nor generic
>> PHY (GENERIC_PHY) can-transceiver binding
>> Documentation/devicetree/bindings/net/can/can-transceiver.yaml which
>> specifies max-bitrate. I don't have strong feelings whether to use
>> max-bitrate or max-speed.
> 
> Okay, max-bitrate is fine.
> 
>>
>> Speaking about Ethernet PHYs, what are to pros and cons to use the
>> generic PHY compared to the Ethernet PHY infrastructure?
> 
> For higher speed ethernet, both are used. There's the serdes phy and
> the ethernet phy with serdes phy using the generic phy binding. For
> CAN, it probably comes down to what's a better fit.
> 
> Rob
>