linux-kernel - Re: [PATCH v4 3/9] usb: dwc3: Increase timeout for CmdAct cleared by device controller

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Message-ID: <e3b0ff51-70ab-7d16-2c7e-cacac7d97043@synopsys.com>
Date:   Tue, 19 May 2020 06:46:17 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Jun Li <jun.li@....com>, Felipe Balbi <balbi@...nel.org>,
        Jun Li <lijun.kernel@...il.com>
CC:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Yu Chen <chenyu56@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        ShuFan Lee <shufan_lee@...htek.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Jack Pham <jackp@...eaurora.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Peter Chen <peter.chen@....com>
Subject: Re: [PATCH v4 3/9] usb: dwc3: Increase timeout for CmdAct cleared by
 device controller

Thinh Nguyen wrote:
> Jun Li wrote:
>>> -----Original Message-----
>>> From: Felipe Balbi <balbif@...il.com> On Behalf Of Felipe Balbi
>>> Sent: 2020年5月16日 19:57
>>> To: Jun Li <jun.li@....com>; Thinh Nguyen <Thinh.Nguyen@...opsys.com>; Jun Li
>>> <lijun.kernel@...il.com>
>>> Cc: John Stultz <john.stultz@...aro.org>; lkml <linux-kernel@...r.kernel.org>; Yu
>>> Chen <chenyu56@...wei.com>; Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Rob
>>> Herring <robh+dt@...nel.org>; Mark Rutland <mark.rutland@....com>; ShuFan Lee
>>> <shufan_lee@...htek.com>; Heikki Krogerus <heikki.krogerus@...ux.intel.com>;
>>> Suzuki K Poulose <suzuki.poulose@....com>; Chunfeng Yun
>>> <chunfeng.yun@...iatek.com>; Hans de Goede <hdegoede@...hat.com>; Andy Shevchenko
>>> <andy.shevchenko@...il.com>; Valentin Schneider <valentin.schneider@....com>;
>>> Jack Pham <jackp@...eaurora.org>; Linux USB List <linux-usb@...r.kernel.org>; open
>>> list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetree@...r.kernel.org>;
>>> Peter Chen <peter.chen@....com>; Thinh Nguyen <Thinh.Nguyen@...opsys.com>
>>> Subject: RE: [PATCH v4 3/9] usb: dwc3: Increase timeout for CmdAct cleared by device
>>> controller
>>>
>>>
>>> Hi,
>>>
>>> Jun Li <jun.li@....com> 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.
> Sorry I made a mistake. You're right. Just checked with one of the RTL
> engineers, and it doesn't need to wake up the phy. However, if it is eSS
> speed, it may take longer time as the command may be completing with the
> suspend clock.
>

What's the value for GCTL[7:6]?

BR,
Thinh