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SubjectRe: (EXT) Re: (EXT) [RFC PATCH v4 03/12] dt-bindings: media: Add bindings for bcm2835-unicam
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Hi Laurent,

Am Samstag, 5. Februar 2022, 03:22:51 CET schrieb Laurent Pinchart:
> Hi Alexander,
>
> On Fri, Feb 04, 2022 at 09:50:06AM +0100, Alexander Stein wrote:
> > Am Donnerstag, 3. Februar 2022, 18:50:00 CET schrieb Jean-Michel Hautbois:
> > > Introduce the dt-bindings documentation for bcm2835 CCP2/CSI2 Unicam
> > > camera interface. Also add a MAINTAINERS entry for it.
> > >
> > > Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> > > Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
> > > Signed-off-by: Jean-Michel Hautbois
> > > <jeanmichel.hautbois@ideasonboard.com>
> > >
> > > ---
> > > v4:
> > > - make MAINTAINERS its own patch
> > > - describe the reg and clocks correctly
> > > - use a vendor entry for the number of data lanes
> > > ---
> > >
> > > .../bindings/media/brcm,bcm2835-unicam.yaml | 110 ++++++++++++++++++
> > > 1 file changed, 110 insertions(+)
> > > create mode 100644
> > >
> > > Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml
> > > b/Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml new
> > > file
> > > mode 100644
> > > index 000000000000..0725a0267c60
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml
> > > @@ -0,0 +1,110 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/media/brcm,bcm2835-unicam.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Broadcom BCM283x Camera Interface (Unicam)
> > > +
> > > +maintainers:
> > > + - Raspberry Pi Kernel Maintenance <kernel-list@raspberrypi.com>
> > > +
> > > +description: |-
> > > + The Unicam block on BCM283x SoCs is the receiver for either
> > > + CSI-2 or CCP2 data from image sensors or similar devices.
> > > +
> > > + The main platform using this SoC is the Raspberry Pi family of
> > > boards.
> > > + On the Pi the VideoCore firmware can also control this hardware
> > > block,
> > > + and driving it from two different processors will cause issues.
> > > + To avoid this, the firmware checks the device tree configuration
> > > + during boot. If it finds device tree nodes starting by csi then
> > > + it will stop the firmware accessing the block, and it can then
> > > + safely be used via the device tree binding.
> > > +
> > > +properties:
> > > + compatible:
> > > + const: brcm,bcm2835-unicam
> > > +
> > > + reg:
> > > + items:
> > > + - description: Unicam block.
> > > + - description: Clock Manager Image (CMI) block.
> > > +
> > > + interrupts:
> > > + maxItems: 1
> > > +
> > > + clocks:
> > > + items:
> > > + - description: Clock to drive the LP state machine of Unicam.
> > > + - description: Clock for the vpu (core clock).
> > > +
> > > + clock-names:
> > > + items:
> > > + - const: lp
> > > + - const: vpu
> > > +
> > > + power-domains:
> > > + items:
> > > + - description: Unicam power domain
> > > +
> > > + brcm,num-data-lanes:
> > > + $ref: /schemas/types.yaml#/definitions/uint32
> > > + enum: [ 2, 4 ]
> > > + description: Number of data lanes on the csi bus
> >
> > There is already data-lanes in
> > Documentation/devicetree/bindings/media/video- interfaces.yaml. AFAICS
> > these two are identical. Can't the video-
> > interface.yaml be used for this? I'm no expert TBH.
>
> This is the number of data lanes that the Unicam instance supports.
> There are two Unicam instances, and they can have 2 or 4 data lanes
> depending on the SoC. The data-lanes endpoint property indicates the
> number of lanes used on a particular board.

Thanks for the explanation. Isn't this something which could be derived from
the compatible, e.g. having 2 different ones for 2 and 4 lanes respectively?
See [1] for a similar situation in the SPI subsystem.
I don't have a strong opinion, just want to share my feedback.

Regards,
Alexander

[1] https://patchwork.kernel.org/project/spi-devel-general/patch/
20211207104114.2720764-1-alexander.stein@ew.tq-group.com/#24641405


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