Re: [PATCH 1/2] dt-bindings: media: qcom,glymur-camss: Use CSIPHY indices for ports

[Bryan O'Donoghue <bod@kernel.org>]

On 05/11/2026 14:01, Loic Poulain wrote:
>>> The CSIPHYs are connected to the CAMSS input ports, which can then be
>>> multiplexed and routed to different CSIDs. The mux identifies its PHY
>>> inputs using the hardware PHY IDs, so the CSIPHY4 is identified as the
>>> CAMSS PHY4 input. In this configuration, PHY2 and PHY3 inputs are not
>>> connected.
>> I could not find that information in Glymur HPG, but maybe I looked
>> wrong. CSID Wrapper lists CSID 0-2, not 0, 1 and 4, but again maybe I am
>> looking at wrong device description/interface...
> Yes, there are three CSIDs (CSID0-2) and two CSID_LITEs
> (CSID_LITE0-1). These blocks select the PHY source to be routed by
> programming their PHY ID (PHY ID = PHY index + 1), as defined by the
> PHY_NUM_SEL field in CSI2_RX_CFG0.
> 
> If the CAMSS port ID matches the PHY index, the port ID can be used
> directly as a routing reference, which keeps the implementation
> straightforward.
> 
> Alternatively, exposing logical port IDs such as { 0, 1, 2 } also
> makes sense. In that case, the driver would simply maintain an
> internal mapping table, for example mapping DT/logical ports { 0, 1, 2
> } to PHY indices { 0, 1, 4 }.

The media-graph informs which PHY connects to which CSID. The 
port-number in the DT really only identifies the fact a PHY input exists 
- it should be considered a mux in front of the set of CSIDs with the 
media-graph being the route.

Since the route is runtime selectable, the media-graph is the boss, not DT.

You can try this on any CAMSS device right now, PHYs connect 
independently to CSI decoders.

PHY_NUM_SEL is derived in the driver, not taken directly from the port 
number: the port indexes csiphy_res[] and csiphy_res[port].csiphy.id is 
the hardware PHY index, e.g. port@3 on x1e is CSIPHY4.

More work should be done to represent the fact-of-life - the mux. This 
was discussed extensively in the standalone PHY series.

The ports being numbered with the PHYs was a consequence of the PHYs 
living inside the CAMSS node - which we have the opportunity now to 
break with and should.

Port number in DT should just be a linear 0-X for the number of PHY 
inputs. Which CSI decoder that port routes to is still a runtime selection.

Honestly I don’t see much value in continuing to treat port numbers as 
hardware mappings in DT now that standalone PHYs have landed.

---
bod