linux-kernel - Re: [PATCH v2] media: dt-bindings: ov8856: decouple lanes and link frequency from driver

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Message-ID: <ZXNy6iGhgP6HZqKJ@kekkonen.localdomain>
Date:   Fri, 8 Dec 2023 19:47:54 +0000
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Maxime Ripard <mripard@...nel.org>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: dt-bindings: ov8856: decouple lanes and link
 frequency from driver

On Fri, Dec 08, 2023 at 08:37:10PM +0100, Krzysztof Kozlowski wrote:
> On 08/12/2023 19:07, Sakari Ailus wrote:
> > Hi Krzysztof,
> > 
> > Thanks for the update.
> > 
> > On Thu, Dec 07, 2023 at 03:23:56PM +0100, Krzysztof Kozlowski wrote:
> >> The data lanes and link frequency were set to match exiting Linux driver
> >> limitations, however bindings should be independent of chosen Linux
> >> driver support.
> >>
> >> Decouple these properties from the driver to match what is actually
> >> supported by the hardware.
> >>
> >> This also fixes DTS example:
> >>
> >>   ov8856.example.dtb: camera@10: port:endpoint:link-frequencies:0: [360000000] is too short
> >>
> >> Fixes: 066a94e28a23 ("media: dt-bindings: media: Use graph and video-interfaces schemas")
> >> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> >>
> >> ---
> >>
> >> Changes in v2:
> >> 1. Rework approach: decouple bindings from driver instead of fixing
> >>    DTS example (Sakari)
> >> ---
> >>  .../devicetree/bindings/media/i2c/ov8856.yaml | 21 +++++++++++--------
> >>  1 file changed, 12 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/media/i2c/ov8856.yaml b/Documentation/devicetree/bindings/media/i2c/ov8856.yaml
> >> index 57f5e48fd8e0..71102a71cf81 100644
> >> --- a/Documentation/devicetree/bindings/media/i2c/ov8856.yaml
> >> +++ b/Documentation/devicetree/bindings/media/i2c/ov8856.yaml
> >> @@ -67,19 +67,22 @@ properties:
> >>  
> >>          properties:
> >>            data-lanes:
> >> -            description: |-
> >> -              The driver only supports four-lane operation.
> >> -            items:
> >> -              - const: 1
> >> -              - const: 2
> >> -              - const: 3
> >> -              - const: 4
> >> +            oneOf:
> >> +              - items:
> >> +                  - const: 1
> >> +              - items:
> >> +                  - const: 1
> >> +                  - const: 2
> >> +              - items:
> >> +                  - const: 1
> >> +                  - const: 2
> >> +                  - const: 3
> >> +                  - const: 4
> >>  
> >>            link-frequencies:
> >>              description: Frequencies listed are driver, not h/w limitations.
> > 
> > This should be dropped, too.
> 
> Ack, I forgot.
> 
> > 
> >> -            maxItems: 2
> >>              items:
> >> -              enum: [ 360000000, 180000000 ]
> >> +              enum: [ 1440000000, 720000000, 360000000, 180000000 ]
> > 
> > These frequencies are listed in the datasheet but they're just an
> > example---the sensor hardware isn't limited to these, the resulting
> > frequency on the CSI-2 bus is simply up to the external clock frequency and
> > PLL configuration. I'd remove the values here altogether.
> 
> Hm, are you sure? Isn't it quite difficult to program device to any
> frequency? But if that's not the case here, I can drop it.

The driver doesn't currently do that, no, but that doesn't mean the
hardware wouldn't support that. There are a few sensor drivers that
calculate the PLL configuration, such as ccs and ov5640.

I'd drop it as it's indeed a driver, not a device limitation.

-- 
Sakari Ailus