Re: [PATCH v5 3/5] dt-bindings: phy: tegra: Add Tegra194 support

[JC Kuo <jckuo@nvidia.com>]

Hi Rob,
For now we have two options.
1. reusing the existing "maximum-speed" which is documented in usb/generic.txt
Pro: no need to add new property
Con: only "super-speed" and "super-speed-plus" are valid for Tegra XUSB PADCTL,
therefore extra code/document change is required.

+	if (device_property_present(&port->dev, "maximum-speed")) {
+		maximum_speed =  usb_get_maximum_speed(&port->dev);
+		if (maximum_speed == USB_SPEED_SUPER)
+			usb3->disable_gen2 = true;
+		else if (maximum_speed == USB_SPEED_SUPER_PLUS)
+			usb3->disable_gen2 = false;
+		else
+			return -EINVAL;
+	}

2. introducing a new proprietary "nvidia,disable-gen2" property
Pro: its logic perfectly matches the need, and code change is minimum

+        usb3->disable_gen2 = of_property_read_bool(np, "nvidia,disable-gen2");

Con: it's a new and proprietary property.

Please let me know which one do you prefer or there is something else works better.

Thanks,
JC


On 1/6/20 3:10 PM, JC Kuo wrote:
> On 1/4/20 6:39 AM, Rob Herring wrote:
>> On Fri, Jan 03, 2020 at 04:18:12PM +0800, JC Kuo wrote:
>>> Extend the bindings to cover the set of features found in Tegra194.
>>> Note that, technically, there are four more supplies connected to the
>>> XUSB pad controller (DVDD_PEX, DVDD_PEX_PLL, HVDD_PEX and HVDD_PEX_PLL)
>>> , but the power sequencing requirements of Tegra194 require these to be
>>> under the control of the PMIC.
>>>
>>> Tegra194 XUSB PADCTL supports up to USB 3.1 Gen 2 speed, however, it
>>> is possible for some platforms have long signal trace that could not
>>> provide sufficient electrical environment for Gen 2 speed. This patch
>>> adds a "maximum-speed" property to usb3 ports which can be used to
>>> specify the maximum supported speed for any particular USB 3.1 port.
>>> For a port that is not capable of SuperSpeedPlus, "maximum-speed"
>>> property should carry "super-speed".
>>>
>>> Signed-off-by: JC Kuo <jckuo@nvidia.com>
>>> ---
>>> Changes in v5:
>>> - re-use "maximum-speed" instead of adding "nvidia,disable-gen2"
>>> Changes in v4: none
>>> Changes in v3: none
>>> Changes in v2:
>>> - fix a typo
>>>
>>>  .../phy/nvidia,tegra124-xusb-padctl.txt        | 18 ++++++++++++++++++
>>>  1 file changed, 18 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
>>> index 9fb682e47c29..7d0089006e67 100644
>>> --- a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
>>> +++ b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
>>> @@ -37,6 +37,7 @@ Required properties:
>>>    - Tegra132: "nvidia,tegra132-xusb-padctl", "nvidia,tegra124-xusb-padctl"
>>>    - Tegra210: "nvidia,tegra210-xusb-padctl"
>>>    - Tegra186: "nvidia,tegra186-xusb-padctl"
>>> +  - Tegra194: "nvidia,tegra194-xusb-padctl"
>>>  - reg: Physical base address and length of the controller's registers.
>>>  - resets: Must contain an entry for each entry in reset-names.
>>>  - reset-names: Must include the following entries:
>>> @@ -62,6 +63,10 @@ For Tegra186:
>>>  - vclamp-usb-supply: Bias rail for USB pad. Must supply 1.8 V.
>>>  - vddio-hsic-supply: HSIC PHY power supply. Must supply 1.2 V.
>>>  
>>> +For Tegra194:
>>> +- avdd-usb-supply: USB I/Os, VBUS, ID, REXT, D+/D- power supply. Must supply
>>> +  3.3 V.
>>> +- vclamp-usb-supply: Bias rail for USB pad. Must supply 1.8 V.
>>>  
>>>  Pad nodes:
>>>  ==========
>>> @@ -154,6 +159,11 @@ For Tegra210, the list of valid PHY nodes is given below:
>>>  - sata: sata-0
>>>    - functions: "usb3-ss", "sata"
>>>  
>>> +For Tegra194, the list of valid PHY nodes is given below:
>>> +- usb2: usb2-0, usb2-1, usb2-2, usb2-3
>>> +  - functions: "xusb"
>>> +- usb3: usb3-0, usb3-1, usb3-2, usb3-3
>>> +  - functions: "xusb"
>>>  
>>>  Port nodes:
>>>  ===========
>>> @@ -221,6 +231,11 @@ Optional properties:
>>>    is internal. In the absence of this property the port is considered to be
>>>    external.
>>>  
>>> +- maximum-speed: Only for Tegra194. A string property that specifies maximum
>>> +  supported speed of a usb3 port. Valid values are:
>>> +  - "super-speed-plus": default, the usb3 port supports USB 3.1 Gen 2 speed.
>>
>> Not defined as a valid value in usb/generic.txt. '-gen2' instead of 
>> '-plus' would be clearer IMO. However, is there any need to define the 
>> maximum speed possible? The purpose of this property is to limit the 
>> speed below the max.
>>
> usb_get_maximum_speed(), which parses "maximum-speed" property, indeed handles
> string "super-speed-plus". Should "super-speed-plus" be documented in
> usb/generic.txt"?
> 
> static const char *const speed_names[] = {
> 	[USB_SPEED_UNKNOWN] = "UNKNOWN",
> 	[USB_SPEED_LOW] = "low-speed",
> 	[USB_SPEED_FULL] = "full-speed",
> 	[USB_SPEED_HIGH] = "high-speed",
> 	[USB_SPEED_WIRELESS] = "wireless",
> 	[USB_SPEED_SUPER] = "super-speed",
> 	[USB_SPEED_SUPER_PLUS] = "super-speed-plus",
> };
> 
> A proprietary "nvidia,disable-gen2" property was proposed in earlier revision to
> "limit the speed below the max". I like it because it fit our needs better and
> requires only one line of code change.
> 
>    usb3->disable_gen2 = of_property_read_bool(np, "nvidia,disable-gen2");
> 
> Should I fallback to that approach?
> 
> Thanks,
> JC
> 
>>> +  - "super-speed": the usb3 port supports USB 3.1 Gen 1 speed only.
>>> +
>>>  For Tegra124 and Tegra132, the XUSB pad controller exposes the following
>>>  ports:
>>>  - 3x USB2: usb2-0, usb2-1, usb2-2
>>> @@ -233,6 +248,9 @@ For Tegra210, the XUSB pad controller exposes the following ports:
>>>  - 2x HSIC: hsic-0, hsic-1
>>>  - 4x super-speed USB: usb3-0, usb3-1, usb3-2, usb3-3
>>>  
>>> +For Tegra194, the XUSB pad controller exposes the following ports:
>>> +- 4x USB2: usb2-0, usb2-1, usb2-2, usb2-3
>>> +- 4x super-speed USB: usb3-0, usb3-1, usb3-2, usb3-3
>>>  
>>>  Examples:
>>>  =========
>>> -- 
>>> 2.17.1
>>>