Re: [PATCH v2 5/5] usb: dwc3: gadget: Increase DWC3 controller halt timeout

From: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
To: Jack Pham <quic_jackp@quicinc.com>, John Keeping <john@metanate.com>
Cc: Wesley Cheng <quic_wcheng@quicinc.com>,
	"balbi@kernel.org" <balbi@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	Thinh Nguyen <Thinh.Nguyen@synopsys.com>, Li Jun <jun.li@nxp.com>
Subject: Re: [PATCH v2 5/5] usb: dwc3: gadget: Increase DWC3 controller halt timeout
Date: Thu, 14 Jul 2022 00:56:24 +0000	[thread overview]
Message-ID: <c3be8cb2-06d0-dd57-078d-7a40be937734@synopsys.com> (raw)
In-Reply-To: <20220713215342.GD8200@jackp-linux.qualcomm.com>

On 7/13/2022, Jack Pham wrote:
> On Wed, Jul 13, 2022 at 12:40:53PM +0100, John Keeping wrote:
>> On Tue, Jul 12, 2022 at 07:56:43PM -0700, Jack Pham wrote:
>>> Hi Wesley,
>>>
>>> On Tue, Jul 12, 2022 at 05:35:23PM -0700, Wesley Cheng wrote:
>>>> Since EP0 transactions need to be completed before the controller halt
>>>> sequence is finished, this may take some time depending on the host and the
>>>> enabled functions.  Increase the controller halt timeout, so that we give
>>>> the controller sufficient time to handle EP0 transfers.
>>>>
>>>> Fixes: 861c010a2ee1 ("usb: dwc3: gadget: Refactor pullup()")
>>>> Suggested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
>>>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>>>> ---
>>>> Link:
>>>>    https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/4988ed34-04a4-060a-ccef-f57790f76a2b@synopsys.com/__;!!A4F2R9G_pg!eidgBYKrTCOm9XSLhpRDscGcM5pkmRIG-XDwBbOYmdcEWUM2MhWJLeeJHhTm8TPNNs9hOgaK1yT8W-0zeZ51Pip-VA$
>>>>
>>>>   drivers/usb/dwc3/gadget.c | 1 +
>>>>   1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>> index 41b7007358de..e32d7293c447 100644
>>>> --- a/drivers/usb/dwc3/gadget.c
>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>> @@ -2476,6 +2476,7 @@ static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
>>>>   	dwc3_gadget_dctl_write_safe(dwc, reg);
>>>>   
>>>>   	do {
>>>> +		msleep(1);
>>> Be aware that this probably won't sleep for *just* 1ms.  From
>>> Documentation/timers/timers-howto.rst:
>>>
>>> 	msleep(1~20) may not do what the caller intends, and
>>> 	will often sleep longer (~20 ms actual sleep for any
>>> 	value given in the 1~20ms range). In many cases this
>>> 	is not the desired behavior.
>>>
>>> So with timeout==500 this loop could very well end up iterating for up
>>> to 10 seconds.  Granted this shouldn't be called from any atomic context
>>> but just wanted to make sure that the effective increase in timeout as
>>> $SUBJECT intends is made clear here and that it's not overly generous.
>>>
>>>>   		reg = dwc3_readl(dwc->regs, DWC3_DSTS);
>>>>   		reg &= DWC3_DSTS_DEVCTRLHLT;
>>>>   	} while (--timeout && !(!is_on ^ !reg));
>> Does it make sense to convert this loop to use read_poll_timeout() and
>> make the timeout explicit, something like:
>>
>> 	ret = read_poll_timeout(dwc3_readl, reg, !(!is_on ^ !(reg & DWC3_DSTS_DEVCTRLHLT)),
>> 				100, timeout * USEC_PER_MSEC, true, dwc->regs, DWC3_DSTS);
>>
>> ?
> Yeah I think it would make sense.  Might even be worthwhile to revisit
> similar loops being performed in dwc3_send_gadget_generic_command() and
> dwc3_send_gadget_ep_cmd() which are currently spinning delay-lessly for a
> fixed number of iterations.
>

++ Jun

BTW, Jun started on this awhile ago. You can review his patch for 
reference if anyone wants to take on this:

https://patchwork.kernel.org/project/linux-usb/patch/1588928985-1585-1-git-send-email-jun.li@nxp.com/

Thanks,
Thinh