Re: [PATCH 06/11] usb: devicetree: dwc3: Introduce num-lanes and lsm

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

Rob Herring wrote:
> On Mon, Jul 20, 2020 at 11:01 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
>> Rob Herring wrote:
>>> On Thu, Jul 16, 2020 at 02:59:08PM -0700, Thinh Nguyen wrote:
>>>> Introduce num-lanes and lane-speed-mantissa-gbps for devices operating
>>>> in super-speed-plus. DWC_usb32 IP supports multiple lanes and can
>>>> operate in different sublink speeds. Currently the device controller
>>>> does not have the information of the phy's number of lanes supported. As
>>>> a result, the user can specify them through these properties if they are
>>>> different than the default setting.
>>>>
>>>> Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
>>>> ---
>>>>    Documentation/devicetree/bindings/usb/dwc3.txt | 9 +++++++++
>>>>    1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> index d03edf9d3935..4eba0615562f 100644
>>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> @@ -86,6 +86,15 @@ Optional properties:
>>>>     - snps,quirk-frame-length-adjustment: Value for GFLADJ_30MHZ field of GFLADJ
>>>>       register for post-silicon frame length adjustment when the
>>>>       fladj_30mhz_sdbnd signal is invalid or incorrect.
>>>> + - snps,num-lanes: set to specify the number of lanes to use. Valid inputs are
>>>> +                    1 or 2. Apply if the maximum-speed is super-speed-plus
>>>> +                    only. Default value is 2 for DWC_usb32. For DWC_usb31,
>>>> +                    it is always 1 at super-speed-plus.
>>>> + - snps,lane-speed-mantissa-gbps: set to specify the symmetric lane speed
>>>> +                    mantissa in Gbps. Valid inputs are 5 or 10. Apply if
>>>> +                    the maximum-speed is super-speed-plus only. Default
>>>> +                    value is 10. For DWC_usb31, it's always 10 at
>>>> +                    super-speed-plus.
>>> This is all common USB things and should be common properties (which we
>>> may already have).
>> Sure. For "num-lanes" is simple, any objection if we use
>> "lane-speed-mantissa-gbps"? Or should we add "lane-speed-exponent"?
> 'num-lanes' is good as that's what PCIe uses. Document that with
> 'maximum-speed'.
>
> I think 'super-speed-plus' should mean gen 2 10G per lane. Then
> between num-lanes and maximum-speed you can define all 4 possible
> rates.

That may confuse the user because now we'd use 'super-speed-plus' to 
define the speed of the lane rather than the device itself.

According to the USB 3.2 spec, super-speed-plus can mean gen2x1, gen1x2, 
or gen2x2.

BR,
Thinh