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

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Message-ID: <CAM5zL5pz0K5ro4-UjiYojM4h9Lqo_af5ZmH1FoZ_ajde_3+Dcg@mail.gmail.com>
Date: Mon, 26 Feb 2024 13:27:35 +0100
From: Paweł Anikiel <panikiel@...gle.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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 Mon, Feb 26, 2024 at 1:07 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> 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.

Okay, thanks for the info. So if I understand correctly, the max link
rate should be represented in bps in the devicetree, and then be
converted to the per 0.27Gbps value by the driver?

One problem is that the values here are too large to be represented in
bps (since the datatype is uint32). Can the property be in Mbps
instead?