linux-kernel - Re: [PATCH v2 9/9] ARM: dts: chameleonv3: Add video device nodes

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Date: Mon, 26 Feb 2024 13:07:51 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Paweł Anikiel <panikiel@...gle.com>
Cc: airlied@...il.com, akpm@...ux-foundation.org, conor+dt@...nel.org,
 daniel@...ll.ch, dinguyen@...nel.org, hverkuil-cisco@...all.nl,
 krzysztof.kozlowski+dt@...aro.org, maarten.lankhorst@...ux.intel.com,
 mchehab@...nel.org, mripard@...nel.org, robh+dt@...nel.org,
 tzimmermann@...e.de, devicetree@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, chromeos-krk-upstreaming@...gle.com,
 ribalda@...omium.org
Subject: Re: [PATCH v2 9/9] ARM: dts: chameleonv3: Add video device nodes

On 26/02/2024 12:09, Paweł Anikiel wrote:
> On Mon, Feb 26, 2024 at 10:15 AM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 21/02/2024 17:02, Paweł Anikiel wrote:
>>> Add device nodes for the video system present on the Chameleon v3.
>>> It consists of six framebuffers and two Intel Displayport receivers.
>>>
>>> Signed-off-by: Paweł Anikiel <panikiel@...gle.com>
>>> ---
>>
>> ...
>>
>>> +             dprx_sst: dp-receiver@...64000 {
>>> +                     compatible = "intel,dprx-20.0.1";
>>> +                     reg = <0xc0064000 0x800>;
>>> +                     interrupt-parent = <&dprx_sst_irq>;
>>> +                     interrupts = <0 IRQ_TYPE_EDGE_RISING>;
>>> +                     intel,max-link-rate = <0x1e>;
>>
>> Rate is not in hex! Rate is in Hz, at least usually...
>>
>> Fix your bindings...
> 
> This is the DisplayPort link rate, for which the allowed values are
> 8.1 Gbps, 5.4 Gbps, 2.7 Gbps, or 1.62 Gbps. The standard way to encode
> them (used in the DisplayPort DPCD registers and this device's

Then it is in bps or some other units:

https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml

> configuration) is by multiples of 0.27Gbps. This value (AFAIK) is
> usually represented in hex, so 8.1Gbps would be 0x1e.

No, the value is represented in logical units. Frequency in Hz. Rate in
bps/kbps/etc. Voltage in volts.

Best regards,
Krzysztof