linux-kernel - Re: [PATCH 17/19] media: dt-bindings: ti,ds90ub960: Add "i2c-addr" link property

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Message-ID: <ffecd7b0-39f1-494b-8a9f-81702a439752@kernel.org>
Date: Wed, 15 Jan 2025 09:40:07 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, Devarsh Thakkar <devarsht@...com>,
 Jai Luthra <jai.luthra@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>, devicetree@...r.kernel.org,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>
Subject: Re: [PATCH 17/19] media: dt-bindings: ti,ds90ub960: Add "i2c-addr"
 link property

On 14/01/2025 12:50, Tomi Valkeinen wrote:
> Hi,
> 
> On 11/01/2025 12:31, Krzysztof Kozlowski wrote:
>> On Fri, Jan 10, 2025 at 11:14:17AM +0200, Tomi Valkeinen wrote:
>>> From: Jai Luthra <jai.luthra@...asonboard.com>
>>>
>>> The serializer's I2C address on the FPD-Link bus is usually communicated
>>> to the deserializer once the forward-channel is established. But in some
>>> cases it might be necessary to program the serializer (over the
>>> back-channel) before the forward-channel is established.
>>>
>>> This can be used e.g. to correct serializer configuration which
>>> otherwise would prevent the FC to be enabled.
>>>
>>> Add a new optional property to specify the I2C address of the
>>> serializer.
>>>
>>> Signed-off-by: Jai Luthra <jai.luthra@...asonboard.com>
>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>>> Cc: devicetree@...r.kernel.org
>>> Cc: Rob Herring <robh@...nel.org>
>>> Cc: Krzysztof Kozlowski <krzk+dt@...nel.org>
>>
>> Why only these folks? Why not all of the maintainers?
> 
> The whole series is sent to the media list and maintainers. I thought 
> this single patch doesn't warrant sending the whole series to DT list 
> and maintainers, so I cc'd them here.


I was wondering why only some of the DT maintainers, not all? My usual
assumption is: you are not using get_maintainers.pl or you are working
on an old kernel.


> 
>> Anyway, Please drop the autogenerated scripts/get_maintainer.pl CC-entries from
>> commit msg. There is no single need to store automated output of
>> get_maintainers.pl in the git log. It can be easily re-created at any
>> given time, thus its presence in the git history is redundant and
>> obfuscates the log.
> 
> I think that's a valid point.
> 
>> If you need it for your own patch management purposes, keep it under the
>> --- separator.
> 
> I'm using b4. I don't know how to do that with b4, but I'll look into it.
> 
>>> ---
>>>   Documentation/devicetree/bindings/media/i2c/ti,ds90ub960.yaml | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/media/i2c/ti,ds90ub960.yaml b/Documentation/devicetree/bindings/media/i2c/ti,ds90ub960.yaml
>>> index 0b71e6f911a8..e17b508b6409 100644
>>> --- a/Documentation/devicetree/bindings/media/i2c/ti,ds90ub960.yaml
>>> +++ b/Documentation/devicetree/bindings/media/i2c/ti,ds90ub960.yaml
>>> @@ -75,6 +75,13 @@ properties:
>>>                 address on the I2C bus where the deserializer resides are
>>>                 forwarded to the serializer.
>>>   
>>> +          i2c-addr:
>>> +            $ref: /schemas/types.yaml#/definitions/uint32
>>
>> Why isn't this part of reg, if that's the same device? If that is not
>> the same device, you are not expected to encode addresses of other
>> devices in this device. Address of 'foo' is not a property of device
>> 'bar'. Phandles or graphs express relationships between devices.
> 
> With the understanding of the HW I have right now, I would have added 
> the i2c address as the address of the serializer node, with reg 
> property. I would probably also do a few other changes to the bindings...
> 
> But as we already have the current bindings, adding the i2c-addr felt 
> like an easy way to keep backwards compatibility and add the address of 
> the serializer.
> 
> However, thinking about this more, maybe we could just go and add the 
> address of the serializer with reg, in the ds90ub953 bindings. It's the 
> ub960 driver that needs the address, but it shouldn't be much trouble to 
> get that from the ub953's data.
> 
> But we need to keep the address optional to keep the backwards 
> compatibility. If it's not defined, the ub960 will automatically receive 
> the serializer's address when the link goes up (as it is handled now).


The 'reg' can grow and should not cause ABI issues, because
implementations should just ignore additional entry.

Best regards,
Krzysztof