RE: [PATCH v4 3/9] usb: dwc3: Increase timeout for CmdAct cleared by device controller

[Jun Li]

> -----Original Message-----
> From: Felipe Balbi <balbif@xxxxxxxxx> On Behalf Of Felipe Balbi
> Sent: 2020年5月16日 19:57
> To: Jun Li <jun.li@xxxxxxx>; Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>; Jun Li
> <lijun.kernel@xxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>; lkml <linux-kernel@xxxxxxxxxxxxxxx>; Yu
> Chen <chenyu56@xxxxxxxxxx>; Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Rob
> Herring <robh+dt@xxxxxxxxxx>; Mark Rutland <mark.rutland@xxxxxxx>; ShuFan Lee
> <shufan_lee@xxxxxxxxxxx>; Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>;
> Suzuki K Poulose <suzuki.poulose@xxxxxxx>; Chunfeng Yun
> <chunfeng.yun@xxxxxxxxxxxx>; Hans de Goede <hdegoede@xxxxxxxxxx>; Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx>; Valentin Schneider <valentin.schneider@xxxxxxx>;
> Jack Pham <jackp@xxxxxxxxxxxxxx>; Linux USB List <linux-usb@xxxxxxxxxxxxxxx>; open
> list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetree@xxxxxxxxxxxxxxx>;
> Peter Chen <peter.chen@xxxxxxx>; Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> Subject: RE: [PATCH v4 3/9] usb: dwc3: Increase timeout for CmdAct cleared by device
> controller
> 
> 
> Hi,
> 
> Jun Li <jun.li@xxxxxxx> writes:
> >> >> Hi Thinh, could you comment this?
> >> >
> >> > You only need to wake up the usb2 phy when issuing the command
> >> > while running in highspeed or below. If you're running in SS or
> >> > higher, internally the controller does it for you for usb3 phy. In
> >> > Jun's case, it seems like it takes longer for his phy to wake up.
> >> >
> >> > IMO, in this case, I think it's fine to increase the command timeout.
> >>
> >> Is there an upper limit to this? Is 32k clock the slowest that can be
> >> fed to the PHY as a suspend clock?
> >
> > Yes, 32K clock is the slowest, Per DWC3 document on Power Down Scale
> > (bits 31:19 of GCTL):
> >
> > "Power Down Scale (PwrDnScale)
> > The USB3 suspend_clk input replaces pipe3_rx_pclk as a clock source to
> > a small part of the USB3 controller that operates when the SS PHY is
> > in its lowest power (P3) state, and therefore does not provide a clock.
> > The Power Down Scale field specifies how many suspend_clk periods fit
> > into a 16 kHz clock period. When performing the division, round up the
> > remainder.
> > For example, when using an 8-bit/16-bit/32-bit PHY and 25-MHz Suspend
> > clock, Power Down Scale = 25000 kHz/16 kHz = 13'd1563 (rounder up)
> > Note:
> > - Minimum Suspend clock frequency is 32 kHz
> > - Maximum Suspend clock frequency is 125 MHz"
> 
> Cool, now do we have an upper bound for how many clock cycles it takes to wake up
> the PHY? 
My understanding is this ep command does not wake up the SS PHY,
the SS PHY still stays at P3 when execute this ep command. The time
required here is to wait controller complete something for this ep
command with 32K clock.

> Then we can just set the time to that upper bound.
Per my test with trace, the time is about 400us(~13 cycles).

Thanks
Li Jun
> 
> --
> balbi