[PATCH] common: usb-hub: Reset hub port before scanning

[Shantur Rathore]

Hi Marek,

On Thu, Nov 23, 2023 at 12:06 AM Marek Vasut <marex at denx.de> wrote:
>
> On 11/20/23 00:03, Shantur Rathore wrote:
> > Hi Marek,
>
> Hi,
>
> > On Sun, Nov 19, 2023 at 8:53 PM Marek Vasut <marex at denx.de> wrote:
> >>
> >> On 11/10/23 15:13, Shantur Rathore wrote:
> >>> Currently when a hub is turned on, all the ports are powered on.
> >>> This works well for hubs which have individual power control.
> >>>
> >>> For the hubs without individual power control this has no effect.
> >>
> >> OK
> >>
> >>> Mostly in these scenarios the hub port is powered before the USB
> >>> controller is enabled, this can lead to some devices in unexpected
> >>> state.
> >>
> >> This ^ part needs clarification.
> >>
> >> Which devices are in incorrect state, the ones connected to the hub
> >> downstream facing ports ?
> >>
> >
> > In my case RockPro64, the power to usb ports onboard is controlled by
> > a regulator.
> > This regulator is enabled as part of init  as here
> > https://github.com/u-boot/u-boot/blob/master/arch/arm/dts/rk3399-rockpro64.dtsi#L177
> >
> > On init, the usb devices connected to the port are powered up, in my
> > case AM8180 (a RTL9210 based ) NVMe to USB enclosure with UAS.
> > But the usb controller is only enabled at 'usb start' and by this time
> > the device is in some state that it doesn't get detected.
> >
> > One way to make sure the devices connected to the ports are in an
> > initialising state is by issuing a port reset before scanning the
> > port.
>
> Why not remove this regulator-always-on and let the PHY driver turn the
> VBUS ON only when it is needed ?
>
> Wouldn't that solve the problem too AND remove unnecessarily enabled
> regulator ?
>
> [...]

Removing the regulator-always-on does make it work but there are few issues

1. regulator is used to control power to multiple ports ( USB3.0 and
USB2.0 in RockPro64 ),
so this could lead to all ports turning off if a phy resets / turns off power
2. Even with regulator-always-on and without this reset port patch,
linux was always
able to detect the drive on the port, so there is something missing in u-boot.
3. Looking at usb hub code in Linux, I found that for USB3.0 it tries
to reset the port before
scanning. The comment says

/* Is a USB 3.0 port in the Inactive or Compliance Mode state?
 * Port warm reset is required to recover
 */

i. https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L5736
ii. https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L2836

I believe this isn't implemented in u-boot and hence explicit reset of
a port fixes the issue.

Kind regards,
Shantur