linux-kernel - Re: [PATCH 2/4] dt-bindings: media: Add bindings for raspberrypi,rp1-cfe

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Message-ID: <aaf0faf8-7041-4510-9e02-1ec896baf4ae@ideasonboard.com>
Date: Tue, 19 Mar 2024 15:56:54 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, Naushir Patuck
 <naush@...pberrypi.com>, Laurent Pinchart
 <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Jacopo Mondi <jacopo.mondi@...asonboard.com>,
 Kieran Bingham <kieran.bingham@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 2/4] dt-bindings: media: Add bindings for
 raspberrypi,rp1-cfe

On 19/03/2024 11:31, Krzysztof Kozlowski wrote:
> On 19/03/2024 07:46, Tomi Valkeinen wrote:
>>>> +  reg:
>>>> +    items:
>>>> +      - description: CSI-2 registers
>>>> +      - description: D-PHY registers
>>>> +      - description: MIPI CFG (a simple top-level mux) registers
>>>> +      - description: FE registers
>>>> +
>>>> +  interrupts:
>>>> +    maxItems: 1
>>>> +
>>>> +  clocks:
>>>> +    maxItems: 1
>>>> +
>>>> +  port:
>>>> +    $ref: /schemas/graph.yaml#/$defs/port-base
>>>> +    additionalProperties: false
>>>> +    description: CSI-2 RX Port
>>>
>>> Only one port, so there is nothing to output to?
>>
>> The CFE has DMA, so it writes to memory. But no other outputs.
> 
> You still might have some sort of pipeline, e.g. some post processing
> block. But if this is end block, then I guess it's fine.

There is a processing block, FE. But it's considered part of the same 
module.

Whether that's exactly correct or not, I'm not sure. I don't have 
detailed hardware docs, but my understanding of the architecture is that 
we have the D-PHY, CSI-2 RX and FE blocks, and a "MIPI CFG" wrapper 
around these (with some CSI-2 & FE muxing and interrupt status flags). 
These are all considered to be part of the same CFE module, and thus we 
represent it here as a single node.

In the patch 4 I explain a bit more about the HW blocks, but maybe it 
would've been beneficial to have some description here too. Here's the 
relevant part:

> +The PiSP Camera Front End (CFE) is a module which combines a CSI-2 receiver with
> +a simple ISP, called the Front End (FE).
> +
> +The CFE has four DMA engines and can write frames from four separate streams
> +received from the CSI-2 to the memory. One of those streams can also be routed
> +directly to the FE, which can do minimal image processing, write two versions
> +(e.g. non-scaled and downscaled versions) of the received frames to memory and
> +provide statistics of the received frames.


>>>> +
>>>> +    properties:
>>>> +      endpoint:
>>>> +        $ref: video-interfaces.yaml#
>>>> +        unevaluatedProperties: false
>>>> +
>>>> +        properties:
>>>> +          data-lanes:
>>>> +            minItems: 1
>>>> +            maxItems: 4
>>>> +
>>>> +          clock-lanes:
>>>> +            maxItems: 1
>>>> +
>>>> +          clock-noncontinuous: true
>>>
>>> Drop
>>
>> Hmm, I saw this used in multiple other bindings, and thought it means
>> the property is allowed and copied it here.
>>
>> If that's not the case, does this mean all the properties from
>> video-interfaces.yaml are allowed (even invalid ones, like pclk-sample)?
> 
> Yes, that's the meaning of unevaluatedProperties you have a bit above.
> 
>>
>>>> +
>>>> +        required:
>>>> +          - clock-lanes
>>>> +          - data-lanes
>>>> +
>>>> +required:
>>>> +  - compatible
>>>> +  - reg
>>>> +  - interrupts
>>>> +  - clocks
>>>> +
>>>> +additionalProperties: false
>>>> +
>>>> +examples:
>>>> +  - |
>>>> +    #include <dt-bindings/clock/rp1.h>
>>>> +    #include <dt-bindings/interrupt-controller/irq.h>
>>>> +    #include <dt-bindings/mfd/rp1.h>
>>>> +
>>>> +    rpi1 {
>>>
>>> soc
>>
>> That should actually be "rp1", not "rpi1". rp1 is the co-processor on
>> which the cfe is located, so it doesn't reside in the soc itself. But
> 
> Where is the co-processor located?

RP1 is a separate chip on the board, behind PCIe. It contains multiple 
blocks, dealing with I/O (like this CSI-2, but also USB, eth, ...). To 
the driver the CFE just shows up as a normal memory mapped IP. Afaics, 
in theory CFE could as well be in the main SoC itself, so, for an 
example, I don't see "soc" as a bad parent node.

  Tomi

>> perhaps that's not relevant, and "soc" is just a generic container that
>> should always be used?
> 
> Does not have to be soc, but rp1 is not generic.
> 
> Node names should be generic. See also an explanation and list of
> examples (not exhaustive) in DT specification:
> https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation
> 
> 
> 
> 
> Best regards,
> Krzysztof
>