Re: [PATCH v3] usb: dwc3: core: Do core softreset when switch mode

[Felipe Balbi <balbi@kernel.org>]

Hi,

John Stultz <john.stultz@linaro.org> writes:
> On Fri, Apr 16, 2021 at 12:49 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
>>
>> John Stultz wrote:
>> > On Fri, Apr 16, 2021 at 3:47 AM Felipe Balbi <balbi@kernel.org> wrote:
>> >>
>> >>
>> >> Hi,
>> >>
>> >> 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
>> >>> switching from host to device. John Stult reported a lockup issue seen
>> >>> with HiKey960 platform without these steps[1]. Similar issue is observed
>> >>> with Ferry's testing platform[2].
>> >>>
>> >>> So, apply the required steps along with some fixes to Yu Chen's and John
>> >>> Stultz's version. The main fixes to their versions are the missing wait
>> >>> for clocks synchronization before clearing GCTL.CoreSoftReset and only
>> >>> apply DCTL.CSftRst when switching from host to device.
>> >>>
>> >>> [1] https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/20210108015115.27920-1-john.stultz@linaro.org/__;!!A4F2R9G_pg!L4TLb25Nkq0DF2qrCPWW13PUq4idhDn5QSZhgvnVAy7wJiYFOSSouSptwo9nOzIdPD4j$
>> >>> [2] https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/0ba7a6ba-e6a7-9cd4-0695-64fc927e01f1@gmail.com/__;!!A4F2R9G_pg!L4TLb25Nkq0DF2qrCPWW13PUq4idhDn5QSZhgvnVAy7wJiYFOSSouSptwo9nO21VT8q7$
>> >>>
>> >>> Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
>> >>> Cc: Ferry Toth <fntoth@gmail.com>
>> >>> Cc: Wesley Cheng <wcheng@codeaurora.org>
>> >>> Cc: <stable@vger.kernel.org>
>> >>> Fixes: 41ce1456e1db ("usb: dwc3: core: make dwc3_set_mode() work properly")
>> >>> Signed-off-by: Yu Chen <chenyu56@huawei.com>
>> >>> Signed-off-by: John Stultz <john.stultz@linaro.org>
>> >>> Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
>> >>
>> >> I still have concerns about the soft reset, but I won't block you guys
>> >> from fixing Hikey's problem :-)
>> >>
>> >> The only thing I would like to confirm is that this has been verified
>> >> with hundreds of swaps happening as quickly as possible. DWC3 should
>> >> still be functional after several hundred swaps.
>> >>
>> >> Can someone confirm this is the case? (I'm assuming this can be
>> >> scripted)
>> >
>> > I unfortunately don't have an easy way to automate the switching right
>> > off. But I'll try to hack up the mux switch driver to provide an
>> > interface we can script against.
>> >
>>
>> FYI, you can do the following:
>>
>> 1) Enable "usb-role-switch" DT property if not already done so
>> 2) Add userspace control:
>>
>> diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
>> index e2b68bb770d1..b203e3d87291 100644
>> --- a/drivers/usb/dwc3/drd.c
>> +++ b/drivers/usb/dwc3/drd.c
>> @@ -555,6 +555,7 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
>>                 mode = DWC3_GCTL_PRTCAP_DEVICE;
>>         }
>>
>> +       dwc3_role_switch.allow_userspace_control = true;
>>         dwc3_role_switch.fwnode = dev_fwnode(dwc->dev);
>>         dwc3_role_switch.set = dwc3_usb_role_switch_set;
>>         dwc3_role_switch.get = dwc3_usb_role_switch_get;
>>
>> 3) Write a script to do the following:
>>
>> # echo host > /sys/class/usb_role/<UDC>/role
>>
>> and
>>
>> # echo device > /sys/class/usb_role/<UDC>/role
>
> Thanks so much for this. So I ran both of those commands in a while
> loop for awhile and didn't see any trouble.
>
> HiKey960 is interesting as well because we have a mux switch, which is
> sort of an intermediary roll switcher (it gets the role switch signal
> from the tcpci_rt1711h, tweaks some gpios and then signals the dwc3).
> So I also did the above tweaks to the mux-switch and had it switching
> between device/none and validated the onboard hub came up and down
> along with the dwc3 core.
>
> Everything still looks good here.

Sounds good, happy to see so many platforms supported by Thinh's
change. Thanks for doing this work, Thinh :-)

-- 
balbi