[PATCH v3 1/2] dt-bindings: display: bridge: add TI TDP158
Marc Gonzalez
mgonzalez at freebox.fr
Wed Jul 24 17:25:03 UTC 2024
On 16/07/2024 11:24, Maxime Ripard wrote:
> On Mon, Jul 15, 2024 at 07:38:34PM GMT, Dmitry Baryshkov wrote:
>> On Mon, 15 Jul 2024 at 17:42, Maxime Ripard <mripard at kernel.org> wrote:
>>> On Mon, Jul 08, 2024 at 11:29:46PM GMT, Dmitry Baryshkov wrote:
>>>> On Mon, Jul 08, 2024 at 04:59:23PM GMT, Maxime Ripard wrote:
>>>>> On Mon, Jul 01, 2024 at 05:36:18PM GMT, Marc Gonzalez wrote:
>>>>>> On 01/07/2024 15:50, Maxime Ripard wrote:
>>>>>>> On Thu, Jun 27, 2024 at 01:13:03PM GMT, Marc Gonzalez wrote:
>>>>>>>
>>>>>>>> TDP158 is an AC-coupled DVI / HDMI to TMDS level shifting Redriver.
>>>>>>>> It supports DVI 1.0, HDMI 1.4b and 2.0b.
>>>>>>>> It supports 4 TMDS channels, HPD, and a DDC interface.
>>>>>>>> It supports dual power supply rails (1.1V on VDD, 3.3V on VCC)
>>>>>>>> for power reduction. Several methods of power management are
>>>>>>>> implemented to reduce overall power consumption.
>>>>>>>> It supports fixed receiver EQ gain using I2C or pin strap to
>>>>>>>> compensate for different lengths input cable or board traces.
>>>>>>>>
>>>>>>>> Features
>>>>>>>>
>>>>>>>> - AC-coupled TMDS or DisplayPort dual-mode physical layer input
>>>>>>>> to HDMI 2.0b TMDS physical layer output supporting up to 6Gbps
>>>>>>>> data rate, compatible with HDMI 2.0b electrical parameters
>>>>>>>> - DisplayPort dual-mode standard version 1.1
>>>>>>>> - Programmable fixed receiver equalizer up to 15.5dB
>>>>>>>> - Global or independent high speed lane control, pre-emphasis
>>>>>>>> and transmit swing, and slew rate control
>>>>>>>> - I2C or pin strap programmable
>>>>>>>> - Configurable as a DisplayPort redriver through I2C
>>>>>>>> - Full lane swap on main lanes
>>>>>>>> - Low power consumption (200 mW at 6Gbps, 8 mW in shutdown)
>>>>>>>>
>>>>>>>> https://www.ti.com/lit/ds/symlink/tdp158.pdf
>>>>>>>>
>>>>>>>> Signed-off-by: Marc Gonzalez <mgonzalez at freebox.fr>
>>>>>>>> ---
>>>>>>>> .../bindings/display/bridge/ti,tdp158.yaml | 51 ++++++++++++++++++++++
>>>>>>>> 1 file changed, 51 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml b/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml
>>>>>>>> new file mode 100644
>>>>>>>> index 0000000000000..21c8585c3bb2d
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/Documentation/devicetree/bindings/display/bridge/ti,tdp158.yaml
>>>>>>>> @@ -0,0 +1,51 @@
>>>>>>>> +# SPDX-License-Identifier: GPL-2.0-only
>>>>>>>> +%YAML 1.2
>>>>>>>> +---
>>>>>>>> +$id: http://devicetree.org/schemas/display/bridge/ti,tdp158.yaml#
>>>>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>>>>> +
>>>>>>>> +title: TI TDP158 HDMI to TMDS Redriver
>>>>>>>> +
>>>>>>>> +maintainers:
>>>>>>>> + - Arnaud Vrac <avrac at freebox.fr>
>>>>>>>> + - Pierre-Hugues Husson <phhusson at freebox.fr>
>>>>>>>> +
>>>>>>>> +properties:
>>>>>>>> + compatible:
>>>>>>>> + const: ti,tdp158
>>>>>>>> +
>>>>>>>> + reg:
>>>>>>>> + description: I2C address of the device
>>>>>>>> +
>>>>>>>> + enable-gpios:
>>>>>>>> + description: GPIO controlling bridge enable
>>>>>>>> +
>>>>>>>> + vcc-supply:
>>>>>>>> + description: Power supply 3.3V
>>>>>>>> +
>>>>>>>> + vdd-supply:
>>>>>>>> + description: Power supply 1.1V
>>>>>>>> +
>>>>>>>> + ports:
>>>>>>>> + $ref: /schemas/graph.yaml#/properties/ports
>>>>>>>> +
>>>>>>>> + properties:
>>>>>>>> + port at 0:
>>>>>>>> + $ref: /schemas/graph.yaml#/properties/port
>>>>>>>> + description: Bridge input
>>>>>>>> +
>>>>>>>> + port at 1:
>>>>>>>> + $ref: /schemas/graph.yaml#/properties/port
>>>>>>>> + description: Bridge output
>>>>>>>> +
>>>>>>>> + required:
>>>>>>>> + - port at 0
>>>>>>>> + - port at 1
>>>>>>>
>>>>>>> The device supports DVI, HDMI or DP input, with various requirements and
>>>>>>> capabilities depending on the input. Your binding doesn't address that.
>>>>>>>
>>>>>>> Similarly, it can do lane-swapping, so we should probably have a
>>>>>>> property to describe what mapping we want to use.
>>>>>>>
>>>>>>> The i2c register access (and the whole behaviour of the device) is
>>>>>>> constrained on the I2C_EN pin status, and you can't read it from the
>>>>>>> device, so it's also something we need to have in the DT.
>>>>>>
>>>>>> We are using the device in its default configuration.
>>>>>> (Power on via OE, then it works as expected)
>>>>>
>>>>> I know, but that doesn't really matter for a binding.
>>>>>
>>>>>> Can we leave any additional properties to be defined by whomever needs
>>>>>> them in the future?
>>>>>
>>>>> If you can guarantee that doing so would be backward compatible, sure.
>>>>> But that means being able to answer those questions with a reasonable
>>>>> plan.
>>>>
>>>> I think proposed bindings are generic enough to cover other possible
>>>> usecases in future.
>>>
>>> I don't think it is. The current binding is for a I2C device that
>>> shouldn't be accessed through I2C.
>>>
>>> It's working for now because the driver doesn't do any access, so it's
>>> all great, but as soon as we add support for the other case, then we'll
>>> have to add a property that states that while it's an i2c device, it
>>> shouldn't be accessed.
>>>
>>> And adding such a property is a compatibility-breaking change.
>>
>> Please correct me if I'm wrong. We have following usecases.
>>
>> 1. I2C_EN pulled low. TI158 is in the pin strap mode, it is not
>> connected to the I2C bus. A0, A1, SDA and SCL pins are used for
>> strapping the settings.
>> board DT file should describe the bridge as a platform device
>> sitting directly under the root node.
>
> DT maintainers have required that reg is always present in the other
> sub-thread.
>
>> 2. I2C_EN pulled high. TI158 is in the I2C mode. It is connected to
>> the I2C bus, A0/A1 pins set the I2C bus address. The device is
>> controlled over the I2C bus
>>
>> 2.a. The same as 2, but the device is not controlled at all, default
>> settings are fine.
>>
>> The driver covers usecase 2.a. The bindings allow extending the driver
>> to the usecase 2 (e.g. via optional properties which specify
>> bord-specific settings)
>>
>> The usecase 1 is a completely separate topic, it requires a different
>> schema file, specifying no i2c address, only voltages supplies and
>> enable-gpios.
>
> I could have mis-unnderstood, but my understanding was that they were
> running it with I2C_EN tied low.
>
> Of course, that's one of the thing that is completely missing from the
> commit log, so who knows.
On our board, the device is sitting on I2C bus blsp2_i2c1.
Therefore, I2C_EN is hard-wired to HIGH.
(As it must be for I2C to function.)
&blsp2_i2c1 {
status = "okay";
tdp158 at 5e {
compatible = "ti,tdp158";
reg = <0x5e>;
enable-gpios = <&tlmm 17 GPIO_ACTIVE_HIGH>;
pinctrl-0 = <&hdmi_en>;
pinctrl-names = "default";
ports {
#address-cells = <1>;
#size-cells = <0>;
port at 0 {
reg = <0>;
tdp158_in: endpoint {
remote-endpoint = <&hdmi_out>;
};
};
port at 1 {
reg = <1>;
tdp158_out: endpoint {
remote-endpoint = <&hdmi_con>;
};
};
};
};
};
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