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

[JC Kuo]

On 1/10/20 7:26 PM, Thierry Reding wrote:
> On Thu, Jan 09, 2020 at 09:31:27AM +0800, JC Kuo wrote:
>> 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.
> 
> I think the first version is much clearer. maximum-speed = "super-speed"
> is very clear and explicit. nvidia,disable-gen2 is less so. While it may
> be true in this case what "disable-gen2" does, using the generic
> bindings has the advantage that it'll be more familiar to people already
> familiar with other USB device tree bindings.
> 
> Also, the nvidia,disable-gen2 property only perfectly matches the need
> because it reflects the name of the variable. If you rewrote the code to
> do something like this:
> 
> 	if (port->maximum_speed <= USB_SPEED_SUPER) {
> 		/* disable gen2 */
> 		...
> 	}

"low-speed/full-speed/high-speed/wireless" options are invalid to a usb3 port
because a usb3 port is not capable of operating at
low-/full-/high-speed/wireless protocols. Therefore,
maximum-speed="low-/full-/high-speed/wireless" is something more like completely
disabling the usb3 port than just disabling super-speed-plus.

I see using an existing "maximum-speed" is preferred. Please review code change
in v5 and let me know if anything could be improved further.

> 
> Then all of a sudden the "maximum-speed" property is a perfect match. In
> general, bindings should be natural to the domain of the bus or device
> that they describe rather than a reflection of how the driver programs
> the device's registers.
> 
> On a side-note: we should also update the usb/generic.txt binding to
> describe the "super-speed-plus" value for the maximum-speed property.
Yes, I feel the same. I will send a patch for it.

Thanks,
JC

> 
> Thierry
> 
>> 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@xxxxxxxxxx>
>>>>> ---
>>>>> 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
>>>>>