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

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Rob Herring wrote:
> On Tue, Jul 21, 2020 at 10:42 AM Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> wrote:
>> Rob Herring wrote:
>>> On Mon, Jul 20, 2020 at 11:01 PM Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>>>>>> ---
>>>>>>     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.
> Then add new strings as needed to make it clear: super-speed-plus-gen1x2
>
> It's obvious that what 'super-speed-plus' means is not clear since
> USB-IF extended its meaning.
>
> Rob

If we introduce a new enum for gen1x2, now we'd have to go back and 
inspect all the checks for all the drivers where for example speed == 
USB_SPEED_SUPER_PLUS. It seems to be more clunky and may introduce more 
bugs.

BR,
Thinh




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