Re: [PATCH] usb: dwc3: core: Do core softreset when switch mode

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

Hi Felipe,

Thinh Nguyen wrote:
> Felipe Balbi wrote:
>>
>> Hi,
>>
>> Thinh Nguyen <Thinh.Nguyen@synopsys.com> writes:
>>>> Thinh Nguyen <Thinh.Nguyen@synopsys.com> writes:
>>>>> From: Yu Chen <chenyu56@huawei.com>
>>>>> From: John Stultz <john.stultz@linaro.org>
>>>>>
>>>>> According to the programming guide, to switch mode for DRD controller,
>>>>> the driver needs to do the following.
>>>>>
>>>>> To switch from device to host:
>>>>> 1. Reset controller with GCTL.CoreSoftReset
>>>>> 2. Set GCTL.PrtCapDir(host mode)
>>>>> 3. Reset the host with USBCMD.HCRESET
>>>>> 4. Then follow up with the initializing host registers sequence
>>>>>
>>>>> To switch from host to device:
>>>>> 1. Reset controller with GCTL.CoreSoftReset
>>>>> 2. Set GCTL.PrtCapDir(device mode)
>>>>> 3. Reset the device with DCTL.CSftRst
>>>>> 4. Then follow up with the initializing registers sequence
>>>>>
>>>>> Currently we're missing step 1) to do GCTL.CoreSoftReset and step 3) of
>>>>
>>>> we're not really missing, it was a deliberate choice :-) The only reason
>>>> why we need the soft reset is because host and gadget registers map to
>>>> the same physical space within dwc3 core. If we cache and restore the
>>>> affected registers, we're good ;-)
>>>
>>> It's part of the programming model. I've already discussed with internal
>>> RTL designers. This is needed, and I've provided the discussion we had
>>> prior also. We have several different devices in the wild that need
>>> this. What is the concern?
>>
>> Timing :-) If anyone wants to support OTG spec, it'll be super hard to
>> guarantee the timing mandated by the spec if we have to go through full
>> reset.
> 
> This is for DRD only. It should not impact the old OTG flow. We already
> have the check in place.
> 
I thought I checked for OTG, but I missed it. I think v3 should cover it.

Thanks,
Thinh