linux-kernel - Re: [PATCH 1/3] dt-bindings: display: bridge: add sam9x7-lvds compatible

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Date: Thu, 1 Feb 2024 08:39:41 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Dharma.B@...rochip.com, robh@...nel.org
Cc: conor@...nel.org, krzk@...nel.org, Manikandan.M@...rochip.com,
 andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, jonas@...boo.se,
 jernej.skrabec@...il.com, airlied@...il.com, daniel@...ll.ch,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Linux4Microchip@...rochip.com
Subject: Re: [PATCH 1/3] dt-bindings: display: bridge: add sam9x7-lvds
 compatible

On 01/02/2024 05:10, Dharma.B@...rochip.com wrote:
> On 31/01/24 12:42 am, Rob Herring wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> On Tue, Jan 23, 2024 at 03:39:13AM +0000, Dharma.B@...rochip.com wrote:
>>> Hi Conor,
>>>
>>> On 22/01/24 10:07 pm, Conor Dooley wrote:
>>>> On Mon, Jan 22, 2024 at 04:51:16PM +0100, Krzysztof Kozlowski wrote:
>>>>> On 22/01/2024 09:29, Dharma Balasubiramani wrote:
>>>>>> Add the 'sam9x7-lvds' compatible binding, which describes the
>>>>>> Low Voltage Differential Signaling (LVDS) Controller found on Microchip's
>>>>>> sam9x7 series System-on-Chip (SoC) devices. This binding will be used to
>>>>>> define the properties and configuration for the LVDS Controller in DT.
>>>>>>
>>>>>> Signed-off-by: Dharma Balasubiramani<dharma.b@...rochip.com>
>>>>>> ---
>>>>>>    .../display/bridge/microchip,sam9x7-lvds.yaml | 59 +++++++++++++++++++
>>>>>>    1 file changed, 59 insertions(+)
>>>>>>    create mode 100644 Documentation/devicetree/bindings/display/bridge/microchip,sam9x7-lvds.yaml
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/display/bridge/microchip,sam9x7-lvds.yaml b/Documentation/devicetree/bindings/display/bridge/microchip,sam9x7-lvds.yaml
>>>>>> new file mode 100644
>>>>>> index 000000000000..8c2c5b858c85
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/display/bridge/microchip,sam9x7-lvds.yaml
>>>>>> @@ -0,0 +1,59 @@
>>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>>> +%YAML 1.2
>>>>>> +---
>>>>>> +$id:http://devicetree.org/schemas/display/bridge/microchip,sam9x7-lvds.yaml#
>>>>>> +$schema:http://devicetree.org/meta-schemas/core.yaml#
>>>>>> +
>>>>>> +title: Microchip SAM9X7 LVDS Controller
>>>>> What is the "X"?
>>>>>
>>>>>> +
>>>>>> +maintainers:
>>>>>> +  - Dharma Balasubiramani<dharma.b@...rochip.com>
>>>>>> +
>>>>>> +description: |
>>>>> Do not need '|' unless you need to preserve formatting.
>>>>>
>>>>>> +  The Low Voltage Differential Signaling Controller (LVDSC) manages data
>>>>>> +  format conversion from the LCD Controller internal DPI bus to OpenLDI
>>>>>> +  LVDS output signals. LVDSC functions include bit mapping, balanced mode
>>>>>> +  management, and serializer.
>>>>>> +
>>>>>> +properties:
>>>>>> +  compatible:
>>>>>> +    const: microchip,sam9x7-lvds
>>>>> What is "x"? Wildcard? Then no, don't use it and instead use proper SoC
>>>>> version number.
>>>> These SoCs actually do have an x in their name. However, and I do always
>>>> get confused here, the sam9x7 is a series of SoCs (the cover letter does
>>>> say this) rather than a specific device.
>>>> I think the series current consists of a sam9x70 sam9x72 and a sam9x75.
>>>> The devices are largely similar, but I am not sure if the sam9x70
>>>> supports LVDS at all. Having a compatible for the series does not seem
>>>> correct to me.
>>> Yes, you are correct. Only sam9x72 and sam9x75 have LVDS support, while
>>> sam9x70 does not. I will revise the compatibility to include both
>>> sam9x72 and sam9x75, as outlined below:
>>>
>>> properties:
>>>     compatible:
>>>       enum:
>>>         - microchip,sam9x72-lvds
>>>         - microchip,sam9x75-lvds
>>
>> I would presume these 2 are the same, but the above implies they
>> aren't. I think what you had is fine assuming these are all
>> fundamentally the same part with just packaging or fused off h/w
>> differences.
> 
> Yes, so is it okay to have compatible for a series? Shall I go ahead with
> "
>    compatible:
>      const: microchip,sam9x7-lvds

You said 9x70, which would match such 9x7 "series", is different, so I
still think series should not be used. I don't know much about Microchip
naming scheme, so this x is always confusing. However if these are the
same, maybe just use sam9x72?

Best regards,
Krzysztof