Re: [PATCH 2/4] Revert "dt-bindings: display: bridge: ldb: Fill in reg property"

Marco Felsch
2026-05-05T15:46:43Z

On 26-05-05, Rob Herring wrote:
> On Mon, May 04, 2026 at 10:21:42PM +0200, Marco Felsch wrote:
> > This reverts commit 16c8d76abe83d75b578d72ee22d25a52c764e14a.
> >
> > Remove the 'reg' and 'reg-names' property from the LDB.
> >
> > The LDB is either part of the IOMUX_GPR (i.MX6SX) or the BLKCTRL
> > (i.MX8MP, i.MX93) register space. Both IOMUX_GPR and BLKCTRL are
> > register ranges with loose register definitions. E.g.
> >
> > - On the i.MX8MP there is one register which controls the AXI
> > threshold for two different IPs (BIT(31:16) - IP1, BIT(15:0) - IP2).
> > - On the i.MX6SX IOMUXC_GPR5 controlls: CSI2 mux, WDOG3 settings, PXP
> > handshake, ...
> >
> > In conclusion: it can't be ensured that one register belongs to one
> > dedicated IP and the LDB is rather an exception than the rule.
>
> It is fine if there's a child node for LDB if the LDB registers are
> consistent, but the other misc things are represented by the parent
> node. It is certainly not a requirement that either everything be in
> child nodes or nothing be in child nodes.
>
> What I don't see in this series is what problem does this fix? If you
> are going to break compatibility, then there had better be a good
> reason.

Hi Rob,

with the upcoming i.MX9x SoCs the parent syscon (BLKCTRL) controlls
multiple other IPs, e.g. a DPI mux added by commit 3feaa4342637
("dt-bindings: soc: imx93-media-blk-ctrl: Add PDFC subnode to schema and
example").

During the discussion of the above commit we agreed that the sub-devices
of the syscon shall not use the reg property due to the fact that one
register serves multiple purposes. In the above case the same register
controlling the dpi-mux also controlls MIPI-DSI bits. The MIPI-DSI bits
can be abstracted as drm-bridge as well. Two sub-devs using the same
'reg' property below the same parent seems odd and I don't know if this
allowed either.

Now the LDB is also part of this BLKCTRL syscon device but requires the
reg property. TBH, I don't know why the reg property was added in the
first place, due to the above fact (multiple sub-devs - same register).

Of course, we could limit the breakage to i.MX9* SoCs only which is done
by:
- https://lore.kernel.org/all/20260329-fsl_ldb_schema_fix-v1-1-351372754bc0@nxp.com/

but I don't think that this would be nice from user and from maintainer
perspective, because:
1) The same LDB "IP" would have a different dt-binding
(user perspective)
2) It introduces another dimension drivers need to care about
(maintainer perspective)

Therefore I went this way to drop it all together to make it easier for
the user and the maintainers.

Regards,
Marco

>
> Rob
>

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