Date:   Mon, 21 Feb 2022 09:10:27 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Jean-Michel Hautbois <jeanmichel.hautbois@...asonboard.com>,
        dave.stevenson@...pberrypi.com, devicetree@...r.kernel.org,
        kernel-list@...pberrypi.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org, lukasz@...y.st,
        mchehab@...nel.org, naush@...pberrypi.com, robh@...nel.org,
        tomi.valkeinen@...asonboard.com,
        bcm-kernel-feedback-list@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH v5 03/11] dt-bindings: media: Add bindings for
 bcm2835-unicam

Hi Stefan,

On Mon, Feb 14, 2022 at 12:32:59PM +0100, Stefan Wahren wrote:
> Am 14.02.22 um 10:54 schrieb Laurent Pinchart:
> > On Mon, Feb 14, 2022 at 10:39:54AM +0100, Maxime Ripard wrote:
> >> On Sun, Feb 13, 2022 at 04:48:45PM +0100, Stefan Wahren wrote:
> >>> as someone with a little more insight to the clocks, i like to know your
> >>> opinion about the bcm2835-unicam binding.
> >>>
> >>> Am 08.02.22 um 16:50 schrieb Jean-Michel Hautbois:
> >>>> Introduce the dt-bindings documentation for bcm2835 CCP2/CSI2 Unicam
> >>>> camera interface.
> >>>>
> >>>> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> >>>> Signed-off-by: Naushir Patuck <naush@...pberrypi.com>
> >>>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@...asonboard.com>
> >>>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.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   | 117 ++++++++++++++++++
> >>>>  1 file changed, 117 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..1938ace23b3d
> >>>> --- /dev/null
> >>>> +++ b/Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml
> >>>> @@ -0,0 +1,117 @@
> >>>> +# 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@...pberrypi.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 whose name starts with '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.
> >>>> +
> >>>> +  reg-names:
> >>>> +    items:
> >>>> +      - const: unicam
> >>>> +      - const: cmi
> >>>> +
> >>>> +  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
> >>>> +
> >>>
> >>> according to this patch [1], the unicam driver only needs the VPU clock
> >>> reference just to enforce a minimum of 250 MHz. The firmware clock
> >>> binding and its driver is specific to the bcm2711, but the Unicam IP
> >>> exists since bcm2835.
> >>>
> >>> So do you think the clock part is correct or should be the VPU clock
> >>> optional?
> >>
> >> I think we should keep it mandatory. Indeed, that clock is shared with
> >> the HVS that will change its rate on a regular basis, so even just
> >> enforcing that 250MHz while it's on without a clock handle will be
> >> fairly hard.
> >>
> >> Also, those are the constraints we have now, but having the clock handle
> >> all the time will allow us to add any constraint we might need in the
> >> future.
> >>
> >> And BCM2711 or not, the clock has probably always been there.
> >
> > Furthermore, regardless of what the driver needs, Unicam operates with
> > the VPU clock, so I think it makes sense to reference it in the device
> > tree.
> 
> okay, as a result we need a DTS patch for bcm2835-rpi.dtsi to enable the
> firmware clocks and its driver in this series.

Can't we do that on top, enabling Unicam support for bcm2711 only first
? I have no idea how to deal with firmware clocks on bcm2825, and I'm
not sure Jean-Michel even has a hardware platform to test it.

If you want to send a patch series to enable firmware clocks on bcm2835,
we'll be happy to rebase on top.

-- 
Regards,

Laurent Pinchart

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