linux-kernel - Re: [PATCH 1/2] dt-bindings: serial: Add bindings for nvidia,tegra264-utc

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Message-ID: <20250128-amusing-squirrel-of-gaiety-b3ba97@krzk-bin>
Date: Tue, 28 Jan 2025 08:52:45 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Kartik Rajput <kkartik@...dia.com>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, thierry.reding@...il.com, 
	jonathanh@...dia.com, hvilleneuve@...onoff.com, arnd@...nel.org, 
	geert+renesas@...der.be, robert.marko@...tura.hr, schnelle@...ux.ibm.com, 
	andriy.shevchenko@...ux.intel.com, linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: serial: Add bindings for
 nvidia,tegra264-utc

On Tue, Jan 28, 2025 at 12:16:32PM +0530, Kartik Rajput wrote:
> The Tegra UTC (UART Trace Controller) is a HW based serial port that
> allows multiplexing multiple data streams of up to 16 UTC clients into
> a single hardware serial port.
> 
> Add bindings for the Tegra UTC client device.
> 
> Signed-off-by: Kartik Rajput <kkartik@...dia.com>
> ---
>  .../bindings/serial/nvidia,tegra264-utc.yaml  | 83 +++++++++++++++++++
>  1 file changed, 83 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/serial/nvidia,tegra264-utc.yaml
> 
> diff --git a/Documentation/devicetree/bindings/serial/nvidia,tegra264-utc.yaml b/Documentation/devicetree/bindings/serial/nvidia,tegra264-utc.yaml
> new file mode 100644
> index 000000000000..63ba3655451f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/serial/nvidia,tegra264-utc.yaml
> @@ -0,0 +1,83 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/serial/nvidia,tegra264-utc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NVIDIA Tegra UART Trace Controller (UTC) client

Controller and client (Client?) sound conflicting. What is this client
of?

> +
> +maintainers:
> +  - Kartik Rajput <kkartik@...dia.com>
> +  - Thierry Reding <thierry.reding@...il.com>
> +  - Jonathan Hunter <jonathanh@...dia.com>
> +
> +description:
> +  The Tegra UTC (UART Trace Controller) is a hardware controller that
> +  allows multiple systems within the Tegra SoC to share a hardware UART
> +  interface. It supports up to 16 clients, with each client having its own
> +  interrupt and a FIFO buffer for both RX (receive) and TX (transmit), each
> +  capable of holding 128 characters.

So is this client or the controller?

> +
> +  The Tegra UTC uses 8-N-1 configuration and operates on a pre-configured
> +  baudrate, which is configured by the bootloader.
> +
> +properties:
> +  $nodename:
> +    pattern: "^serial(@.*)?$"

Drop, not needed. But you miss proper $ref, see other bindings.


> +
> +  compatible:
> +    const: nvidia,tegra264-utc
> +
> +  reg:
> +    items:
> +      - description: Register region for TX client.

Drop redundant parts, so just "TX region".

> +      - description: Register region for RX client.
> +    minItems: 2

Drop

> +
> +  reg-names:
> +    items:
> +      - const: tx
> +      - const: rx
> +    minItems: 2

Drop. Please take a look at other bindings how they do things. There is
no such code anywhere in the kernel.

> +
> +  interrupts:
> +    maxItems: 1
> +
> +  current-speed:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      This property specifies the baudrate at which the Tegra UTC is

Drop "This property specifies the". Do not say what Devicetree syntax
is. We all know. This is a description of hardware, not the DTS langauge.

> +      operating.
> +
> +  nvidia,utc-fifo-threshold:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      This property specifies the UTC TX and RX client FIFO threshold in
> +      terms of occupancy.
> +
> +      This property should have the same value as the burst size (number
> +      of characters read by the Tegra UTC hardware at a time from each
> +      client) which is configured by the bootloader.

Title says this is a client, so quite confusing. Anyway, why is this
board specific?

Also, missing constraints, missing units. Why common serial properties
are not applicable?

Best regards,
Krzysztof