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From: =?UTF-8?Q?Pawe=C5=82_Anikiel?= <panikiel@google.com>
Date: Tue, 27 Feb 2024 12:26:30 +0100
Message-ID: <CAM5zL5rDKMbgN7P=KF2ZayN5ipUB7AYpVccZdLunSUNTR4_f1A@mail.gmail.com>
Subject: Re: [PATCH v2 9/9] ARM: dts: chameleonv3: Add video device nodes
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: airlied@gmail.com, akpm@linux-foundation.org, conor+dt@kernel.org, 
	daniel@ffwll.ch, dinguyen@kernel.org, hverkuil-cisco@xs4all.nl, 
	krzysztof.kozlowski+dt@linaro.org, maarten.lankhorst@linux.intel.com, 
	mchehab@kernel.org, mripard@kernel.org, robh+dt@kernel.org, 
	tzimmermann@suse.de, devicetree@vger.kernel.org, 
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, 
	linux-media@vger.kernel.org, chromeos-krk-upstreaming@google.com, 
	ribalda@chromium.org
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On Mon, Feb 26, 2024 at 6:30=E2=80=AFPM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 26/02/2024 13:27, Pawe=C5=82 Anikiel wrote:
> > On Mon, Feb 26, 2024 at 1:07=E2=80=AFPM Krzysztof Kozlowski
> > <krzysztof.kozlowski@linaro.org> wrote:
> >>
> >> On 26/02/2024 12:09, Pawe=C5=82 Anikiel wrote:
> >>> On Mon, Feb 26, 2024 at 10:15=E2=80=AFAM Krzysztof Kozlowski
> >>> <krzysztof.kozlowski@linaro.org> wrote:
> >>>>
> >>>> On 21/02/2024 17:02, Pawe=C5=82 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: Pawe=C5=82 Anikiel <panikiel@google.com>
> >>>>> ---
> >>>>
> >>>> ...
> >>>>
> >>>>> +             dprx_sst: dp-receiver@c0064000 {
> >>>>> +                     compatible =3D "intel,dprx-20.0.1";
> >>>>> +                     reg =3D <0xc0064000 0x800>;
> >>>>> +                     interrupt-parent =3D <&dprx_sst_irq>;
> >>>>> +                     interrupts =3D <0 IRQ_TYPE_EDGE_RISING>;
> >>>>> +                     intel,max-link-rate =3D <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 encod=
e
> >>> 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 i=
n
> >> 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
>
> or kbps

The one that's already present in dtschema is kBps (kilobytes per
second) which isn't right for this case IMO.

>
> > converted to the per 0.27Gbps value by the driver?
>
> If driver needs some register-based value, then yes.
>
> >
> > 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?
>
> Can be. You can submit a patch to dtschema (patch to DT spec list or
> github pull request) adding '-mbps' as well.

I sent a PR with both kbps and mbps.