linux-kernel - Re: [PATCH] media: dt-bindings: qcom,sm8550-iris: Do not reference legacy venus properties

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Message-ID: <20250825123620.wxf6x6ep6jm3oykm@hu-mojha-hyd.qualcomm.com>
Date: Mon, 25 Aug 2025 18:06:20 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Vikash Garodia <quic_vgarodia@...cinc.com>,
        Dikshita Agarwal <quic_dikshita@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        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>, linux-arm-msm@...r.kernel.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: dt-bindings: qcom,sm8550-iris: Do not reference
 legacy venus properties

On Mon, Aug 25, 2025 at 02:02:56PM +0200, Krzysztof Kozlowski wrote:
> On 25/08/2025 13:37, Mukesh Ojha wrote:
> > On Sat, Aug 23, 2025 at 05:53:50PM +0200, Krzysztof Kozlowski wrote:
> >> The Qualcomm SoC Iris video codec is an evolution of previous Venus and
> >> it comes with its own Iris Linux drivers.  These new drivers were
> >> accepted under condition they actually improve state of afairs, instead
> >> of duplicating old, legacy solutions.
> >>
> >> Unfortunately binding still references common parts of Venus without
> >> actual need and benefit.  For example Iris does not use fake
> >> "video-firmware" device node (fake because there is no actual device
> >> underlying it and it was added only to work around some Linux issues
> >> with IOMMU mappings).
> >>
> >> Stop referencing venus-common schema in the new Qualcomm Iris bindings
> >> and move all necessary properties, except unused "video-firmware" (no
> >> driver usage, no DTS).
> >>
> >> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> >> ---
> >>  .../devicetree/bindings/media/qcom,sm8550-iris.yaml | 13 ++++++++++++-
> >>  1 file changed, 12 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> >> index c79bf2101812..320227f437a1 100644
> >> --- a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> >> +++ b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> >> @@ -26,6 +26,9 @@ properties:
> >>            - qcom,sm8550-iris
> >>            - qcom,sm8650-iris
> >>  
> >> +  reg:
> >> +    maxItems: 1
> >> +
> >>    power-domains:
> >>      maxItems: 4
> >>  
> >> @@ -45,6 +48,12 @@ properties:
> >>        - const: core
> >>        - const: vcodec0_core
> >>  
> >> +  firmware-name:
> >> +    maxItems: 1
> >> +
> >> +  interrupts:
> >> +    maxItems: 1
> >> +
> >>    interconnects:
> >>      maxItems: 2
> >>  
> >> @@ -69,6 +78,9 @@ properties:
> >>  
> >>    dma-coherent: true
> >>  
> >> +  memory-region:
> >> +    maxItems: 1
> >> +
> >>    operating-points-v2: true
> >>  
> >>    opp-table:
> >> @@ -85,7 +97,6 @@ required:
> >>    - dma-coherent
> >>  
> >>  allOf:
> >> -  - $ref: qcom,venus-common.yaml#
> >>    - if:
> > 
> > Saw your reply on 
> > https://lore.kernel.org/lkml/59951c47-1015-4598-a885-25f8f1a27c64@kernel.org/
> > 
> > Just trying to understand ABI here, how all of a sudden we remove a binding
> > for a hardware just because it did not get noticed until yet that as it is
> > not a real device and we always say device tree binding should not depend on
> > drivers but the device but we are saying Iris does not use fake "video-firmware"
> > device node for removal. I am a bit confused.
> 
> About what? What is unclear in standard DT ABI rules?
> 
i.e., If a driver is not using a particular binding at any time, its binding
can be removed.

> > 
> > Whether removing will not break any ABI as initial binding enables the IRIS
> > related code to use video-firmware, now we are removing it.
> > I believe, removing binding always break ABI ? or is it depend on driver
> > code not using it ?
> 
> There is no single user of this, out of tree (I briefly checked) and
> in-tree, so there is no ABI impact. I am changing the documentation of
> the ABI, but there is no actual ABI break because impact is 0.

Something is unclear, that is why you are willing to change.

> 
> I am really sorry but it seems you ask about basics of DT, so please
> first get into docs and other existing discussions.

You are right, I'm learning and not an expert.

> 
> Best regards,
> Krzysztof

-- 
-Mukesh Ojha