[PATCH v4 1/3] media: dt-bindings: rockchip,vdec: Add alternative reg-names order for RK35{76,88}

[Conor Dooley]

On Thu, Feb 26, 2026 at 02:45:11PM -0500, Nicolas Dufresne wrote:
> Le jeudi 26 février 2026 à 18:43 +0000, Conor Dooley a écrit :
> > On Thu, Feb 26, 2026 at 12:46:53PM +0200, Cristian Ciocaltea wrote:
> > > With the introduction of the RK3588 SoC, and RK3576 afterwards, two more
> > > register blocks have been provided for the video decoder unit.
> > > 
> > > However, the binding does not properly describe the new hardware layout,
> > > as it breaks the convention expecting the unit address to indicate the
> > > start of the first register range, i.e. 'function' block is listed
> > > before 'link' instead of the opposite.
> > 
> > I don't understand this commit message or rationale for an ABI break.
> > Changing the unit address seems like a "free" fix to your problem,
> > especially when reg-names is not a required property that you can rely
> > on. Actually, there may be a bug in the driver - it expects reg-names
> > for rk3576-vdec and rk3588-vdec but the binding doesn't mandate their
> > presence for those devices.
> 
> If the bindings had been held instead of released early, the order would be what
> is done in this patch for sure, and no one would have complained. These binding
> have never been used by anyone so far, and what you are asking is to create a

20:35:32 conor /stuff/linux$ rg "rk3576-vdec"

arch/arm64/boot/dts/rockchip/rk3576.dtsi
1283:			compatible = "rockchip,rk3576-vdec";

20:35:34 conor /stuff/linux$ rg rk3588-vdec

arch/arm64/boot/dts/rockchip/rk3588-base.dtsi
1357:		compatible = "rockchip,rk3588-vdec";
1389:		compatible = "rockchip,rk3588-vdec";

These look like users, at least at first look. Some elaboration on that
would be good - impact on users definitely should be covered in the
commit message of an ABI break.

> DTS that deviate from the vendor provided documentation for the IP base address.
> I know you have all technical fancy reasoning, but I like when things are
> functional and effective to work with.

FWIW, I don't think you were trying to be dismissive, just trying to
make a valid point about usability being important, but providing clear
justifications for why the order of properties should be changed (or
other similar ABI breaks) is really important. This is v4, and the
rationale you've given here about the documentation, which is the actual
motivation for changing things around, doesn't appear in the commit
message, even after a back and forth with Krzysztof in an earlier
version.

> > Deprecating the order also makes little sense to me, given that some of
> > these devices only have one reg entry, which as far as I can tell from
> > looking at the driver *is* the "function" region, so it can never be
> > entirely deprecated.
> 
> What I'd like to see, is a binding expression that behave like a set, not a
> list, and leave the ordering open. As people keep repeating, there is nothing in
> a binding that assist to define the right ordering (its not address or base
> addres aware). That basically means, we can't as reviewer see that ordering is
> going to imposing using a base address in the unit name (which is a convenience,
> not a rule I suppose) that differ from the vendor documented base address.
> 
> By explicitly removing the ordering in the binding, we create a strict rule that
> driver should retrieve this by name, and never assume the ordering, which I
> personally like.
> 
> thoughts ?

Yeah, you can do this, but to avoid potential breaks you have to do it
from the start, not after the fact. Probably there's bindings that get
acked every day that do do this. Even the retcon is okay to do when
reg-names is mandated by the binding and the users use reg-names in my
opinion.

In this case, the driver is currently buggy, because, as I mentioned, it
uses reg-names without reg-names being required on the platforms with
more than 1 reg property. Probably the binding should make reg-names
mandatory for these platforms even without this patch, but it *has* to
IMO for this proposed change to be applicable.

But anyway, the takeaway from my original mail should be "Conor is not
happy with the rationale the commit message provides for this change,
as it doesn't explain why you want to do it". I necessarily object to
the change itself.

Conor.

> > > Since the binding changes have been already released and a fix would
> > > bring up an ABI break, mark the current 'reg-names' ordering as
> > > deprecated and introduce an alternative 'link,function,cache' listing
> > > which follows the address-based ordering according to the TRM.
> > > 
> > > Additionally, drop the 'reg' description items as the order is not fixed
> > > anymore, while the information they offer is not very relevant anyway.
> > > 
> > > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea at collabora.com>
> > > ---
> > >  .../devicetree/bindings/media/rockchip,vdec.yaml     | 20 ++++++++++++-----
> > > ---
> > >  1 file changed, 12 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/media/rockchip,vdec.yaml
> > > b/Documentation/devicetree/bindings/media/rockchip,vdec.yaml
> > > index 809fda45b3bd..c513b68d2c72 100644
> > > --- a/Documentation/devicetree/bindings/media/rockchip,vdec.yaml
> > > +++ b/Documentation/devicetree/bindings/media/rockchip,vdec.yaml
> > > @@ -28,16 +28,20 @@ properties:
> > >  
> > >    reg:
> > >      minItems: 1
> > > -    items:
> > > -      - description: The function configuration registers base
> > > -      - description: The link table configuration registers base
> > > -      - description: The cache configuration registers base
> > > +    maxItems: 3
> > >  
> > >    reg-names:
> > > -    items:
> > > -      - const: function
> > > -      - const: link
> > > -      - const: cache
> > > +    oneOf:
> > > +      - items:
> > > +          - const: link
> > > +          - const: function
> > > +          - const: cache
> > > +      - items:
> > > +          - const: function
> > > +          - const: link
> > > +          - const: cache
> > > +        deprecated: true
> > > +        description: Use link,function,cache block order instead.
> > >  
> > >    interrupts:
> > >      maxItems: 1
> > > 
> > > -- 
> > > 2.52.0
> > > 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 228 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-rockchip/attachments/20260226/714d3430/attachment.sig>