Hi,

John Stultz [off-list ref] writes:

On Fri, Apr 16, 2021 at 12:49 PM Thinh Nguyen [off-list ref] wrote:

quoted

John Stultz wrote:

quoted

On Fri, Apr 16, 2021 at 3:47 AM Felipe Balbi [off-list ref] wrote:

quoted

Hi,

Thinh Nguyen [off-list ref] writes:

quoted

From: Yu Chen <chenyu56@huawei.com>
From: John Stultz <redacted>

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 <redacted>
Cc: Ferry Toth <redacted>
Cc: Wesley Cheng <redacted>
Cc: <redacted>
Fixes: 41ce1456e1db ("usb: dwc3: core: make dwc3_set_mode() work properly")
Signed-off-by: Yu Chen <chenyu56@huawei.com>
Signed-off-by: John Stultz <redacted>
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