linux-kernel - Re: [PATCH v2 3/3] usb: dwc3: gadget: Add support for disabling U1 and U2 entries

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Date:   Tue, 14 May 2019 21:40:50 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Anurag Kumar Vulisha <anuragku@...inx.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Felipe Balbi" <balbi@...nel.org>,
        "Claus H. Stovgaard" <cst@...seone.com>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "v.anuragkumar@...il.com" <v.anuragkumar@...il.com>
Subject: Re: [PATCH v2 3/3] usb: dwc3: gadget: Add support for disabling U1
 and U2 entries

Hi Anurag,

Anurag Kumar Vulisha wrote:
> Hi Thinh,
>
>> -----Original Message-----
>> From: Thinh Nguyen [mailto:Thinh.Nguyen@...opsys.com]
>> Sent: Saturday, May 11, 2019 7:18 AM
>> To: Anurag Kumar Vulisha <anuragku@...inx.com>; Thinh Nguyen
>> <Thinh.Nguyen@...opsys.com>; Greg Kroah-Hartman
>> <gregkh@...uxfoundation.org>; Rob Herring <robh+dt@...nel.org>; Mark Rutland
>> <mark.rutland@....com>; Felipe Balbi <balbi@...nel.org>; Claus H. Stovgaard
>> <cst@...seone.com>
>> Cc: linux-usb@...r.kernel.org; devicetree@...r.kernel.org; linux-
>> kernel@...r.kernel.org; v.anuragkumar@...il.com
>> Subject: Re: [PATCH v2 3/3] usb: dwc3: gadget: Add support for disabling U1 and U2
>> entries
>>
>> Hi,
>>
>> Anurag Kumar Vulisha wrote:
>>> Hi Thinh,
>>>
>>>> -----Original Message-----
>>>> From: Thinh Nguyen [mailto:Thinh.Nguyen@...opsys.com]
>>>> Sent: Friday, May 10, 2019 5:30 AM
>>>> To: Anurag Kumar Vulisha <anuragku@...inx.com>; Thinh Nguyen
>>>> <Thinh.Nguyen@...opsys.com>; Greg Kroah-Hartman
>>>> <gregkh@...uxfoundation.org>; Rob Herring <robh+dt@...nel.org>; Mark Rutland
>>>> <mark.rutland@....com>; Felipe Balbi <balbi@...nel.org>; Claus H. Stovgaard
>>>> <cst@...seone.com>
>>>> Cc: linux-usb@...r.kernel.org; devicetree@...r.kernel.org; linux-
>>>> kernel@...r.kernel.org; v.anuragkumar@...il.com
>>>> Subject: Re: [PATCH v2 3/3] usb: dwc3: gadget: Add support for disabling U1 and
>> U2
>>>> entries
>>>>
>>>> Hi Anurag,
>>>>
>>>> Anurag Kumar Vulisha wrote:
>>>>>>> +		return -EINVAL;
>>>>>>>
>>>>>>>  	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
>>>>>>>  	if (set)
>>>>>>> @@ -626,7 +630,10 @@ static int dwc3_ep0_set_config(struct dwc3 *dwc,
>>>> struct
>>>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>>>> index e293400..f2d3112 100644
>>>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>>>> @@ -2073,6 +2073,24 @@ static int dwc3_gadget_stop(struct usb_gadget *g)
>>>>>>>  	return 0;
>>>>>>>  }
>>>>>>>
>>>>>>> +static void dwc3_gadget_config_params(struct usb_gadget *g,
>>>>>>> +				      struct usb_dcd_config_params *params)
>>>>>>> +{
>>>>>>> +	struct dwc3		*dwc = gadget_to_dwc(g);
>>>>>>> +
>>>>>>> +	/* U1 Device exit Latency */
>>>>>>> +	if (dwc->dis_u1_entry_quirk)
>>>>>>> +		params->bU1devExitLat = 0;
>>>>>> It doesn't make sense to have exit latency of 0. Rejecting
>>>>>> SET_FEATURE(enable U1/U2) should already let the host know that the
>>>>>> device doesn't support U1/U2.
>>>>>>
>>>>> I am okay to remove this, but I feel that it is better to report zero value instead
>>>>> of a non-zero value in exit latency of BOS when U1 or U2 entries are not
>> supported.
>>>>> Advantage of reporting 0 is that some hosts doesn't even send
>>>> SET_FEATURE(U1/U2)
>>>>> requests on seeing zero value in BOS descriptor. Also there can be cases where
>> U1 is
>>>>> disabled and U2 entry is allowed or vice versa, for these kind of cases the driver
>> can
>>>>> set zero exit latency value for U1 and non-zero exit latency value for U2 . Based
>> on
>>>> this
>>>>> I think it would be better to report 0 when U1/U2 states are not enabled. Please
>>>> provide
>>>>> your opinion on this.
>>>> Hm... I assume you're testing against linux usb stack and xhci host. If
>>>> that's the case, it looks like host will still request the device to
>>>> enter U1/U2 despite the device rejecting SET_FEATURE(enable U1/U2). This
>>>> needs to be fixed. I think what you have is fine to workaround this issue.
>>> Thanks . Will send the next series with the other fixes that you have suggested
>>>
>>> Best Regards,
>>> Anurag Kumar Vulisha
>>>
>> I want to try something. Can you see if this helps with your performance
>> test without setting the U1/U2 exit latency to 0?
>> (No need to change what you have in your patch. This is just for testing).
>>
> With your patch , the link doesn't enter into U1/U2 and I am also getting
> better performance
>
> Thanks,
> Anurag Kumar Vulisha

Thanks for testing.

BR,
Thinh