linux-kernel - Re: [PATCH 1/2] media: dt-bindings: Remove assigned-clock-* from various schema

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Message-ID: <b0154e75-370e-4a5f-9309-6a3ae5d85b5c@kernel.org>
Date: Tue, 15 Oct 2024 08:13:19 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Dave Stevenson <dave.stevenson@...pberrypi.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>, Shawn Guo
 <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Martin Kepplinger <martink@...teo.de>,
 Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
 "Paul J. Murphy" <paul.j.murphy@...el.com>,
 Daniele Alessandrelli <daniele.alessandrelli@...el.com>,
 Tommaso Merciai <tomm.merciai@...il.com>,
 Martin Hecht <martin.hecht@...et.eu>, Zhi Mao <zhi.mao@...iatek.com>,
 Alain Volmat <alain.volmat@...s.st.com>,
 Mikhail Rudenko <mike.rudenko@...il.com>,
 Ricardo Ribalda <ribalda@...nel.org>,
 Kieran Bingham <kieran.bingham@...asonboard.com>,
 Umang Jain <umang.jain@...asonboard.com>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
 Dongchun Zhu <dongchun.zhu@...iatek.com>,
 Quentin Schulz <quentin.schulz@...obroma-systems.com>,
 Todor Tomov <todor.too@...il.com>, linux-media@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] media: dt-bindings: Remove assigned-clock-* from
 various schema

On 14/10/2024 22:34, Laurent Pinchart wrote:
> On Mon, Oct 14, 2024 at 09:43:07AM +0200, Krzysztof Kozlowski wrote:
>> On Sat, Oct 12, 2024 at 04:02:50PM +0100, Bryan O'Donoghue wrote:
>>> Remove extraneous assigned-clock* from media/i2c/* schemas, retain in the
>>> relevant examples.
>>>
>>> Link: https://lore.kernel.org/linux-media/j7kgz2lyxnler5qwd7yiazdq6fmsv77kyozdrxf33h54ydakjz@uqjhwhoyv6re
>>> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>>> ---
>>>  Documentation/devicetree/bindings/media/i2c/hynix,hi846.yaml | 8 --------
>>>  Documentation/devicetree/bindings/media/i2c/ovti,ov5648.yaml | 8 --------
>>>  Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml | 8 --------
>>>  Documentation/devicetree/bindings/media/i2c/ovti,ov9282.yaml | 4 ----
>>>  Documentation/devicetree/bindings/media/i2c/sony,imx258.yaml | 4 ----
>>>  Documentation/devicetree/bindings/media/i2c/sony,imx334.yaml | 4 ----
>>>  Documentation/devicetree/bindings/media/i2c/sony,imx335.yaml | 4 ----
>>>  Documentation/devicetree/bindings/media/i2c/sony,imx412.yaml | 4 ----
>>>  8 files changed, 44 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/media/i2c/hynix,hi846.yaml b/Documentation/devicetree/bindings/media/i2c/hynix,hi846.yaml
>>> index 60f19e1152b33128cf3baa15b8c70a874ca6d52e..d18ead8f7fc43bfacc291aed85b5ca9166c46edb 100644
>>> --- a/Documentation/devicetree/bindings/media/i2c/hynix,hi846.yaml
>>> +++ b/Documentation/devicetree/bindings/media/i2c/hynix,hi846.yaml
>>> @@ -28,12 +28,6 @@ properties:
>>>      items:
>>>        - description: Reference to the mclk clock.
>>>  
>>> -  assigned-clocks:
>>> -    maxItems: 1
>>> -
>>> -  assigned-clock-rates:
>>> -    maxItems: 1
>>> -
>>>    reset-gpios:
>>>      description: Reference to the GPIO connected to the RESETB pin. Active low.
>>>      maxItems: 1
>>> @@ -82,8 +76,6 @@ required:
>>>    - compatible
>>>    - reg
>>>    - clocks
>>> -  - assigned-clocks
>>> -  - assigned-clock-rates
>>
>> That's not extraneous, but has a meaning that without assigned-clocks
>> this device or driver will not operate.
> 
> How so ? Even if we assume that the device requires a specific clock
> frequency (which is often not the case for camera sensors, the
> limitation usually comes from drivers, so the constraint shouldn't be
> expressed in the bindings in that case), there is no overall requirement
> to assign a clock rate as in many cases the clock will come from a
> fixed-frequency oscillator. This seems to be a constraint that is
> outside of the scope of DT bindings. It is similar to regulators, where
> the regulator consumer doesn't have a way to express supported voltages
> in its DT bindings.

This property does not say it comes from a fixed-frequency oscillator,
so I do not understand why you think it is unreasonable constraint. I
have no clue what the author wanted to say here, so I just explained
that there is a meaning behind requiring such properties. If you claim
device or implementations do not have such requirement, after
investigating each case, feel free to drop this. I think I also stated
this already in other reply.

Best regards,
Krzysztof