linux-kernel - Re: [PATCH v3 2/2] usb: dwc3: Fix DRD mode change sequence following programming guide

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Message-ID: <e696b018-b310-5811-5c80-3c50dde297e7@synopsys.com>
Date:   Sat, 6 Mar 2021 23:39:01 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <wcheng@...eaurora.org>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>
CC:     Felipe Balbi <balbi@...nel.org>,
        Tejas Joglekar <Tejas.Joglekar@...opsys.com>,
        Yang Fei <fei.yang@...el.com>,
        YongQin Liu <yongqin.liu@...aro.org>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Jun Li <lijun.kernel@...il.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] usb: dwc3: Fix DRD mode change sequence following
 programming guide

Wesley Cheng wrote:
>
> On 1/7/2021 5:51 PM, John Stultz wrote:
>> In reviewing the previous patch, Thinh Nguyen pointed out that
>> the DRD mode change sequence should be like the following when
>> switching from host -> device according to the programming guide
>> (for all DRD IPs):
>> 1. Reset controller with GCTL.CoreSoftReset
>> 2. Set GCTL.PrtCapDir(device)
>> 3. Soft reset with DCTL.CSftRst
>> 4. Then follow up with the initializing registers sequence
>>
>> The current code does:
>> a. Soft reset with DCTL.CSftRst on driver probe
>> b. Reset controller with GCTL.CoreSoftReset (added in previous
>>    patch)
>> c. Set GCTL.PrtCapDir(device)
>> d. < missing DCTL.CSftRst >
>> e. Then follow up with initializing registers sequence
>>
>> So this patch adds the DCTL.CSftRst soft reset that was currently
>> missing from the dwc3 mode switching.
>>
>> Cc: Felipe Balbi <balbi@...nel.org>
>> Cc: Tejas Joglekar <tejas.joglekar@...opsys.com>
>> Cc: Yang Fei <fei.yang@...el.com>
>> Cc: YongQin Liu <yongqin.liu@...aro.org>
>> Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
>> Cc: Thinh Nguyen <thinhn@...opsys.com>
>> Cc: Jun Li <lijun.kernel@...il.com>
>> Cc: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: linux-usb@...r.kernel.org
>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>> ---
>> Feedback would be appreciated. I'm a little worried I should be
>> conditionalizing the DCTL.CSftRst on DRD mode controllers, but
>> I'm really not sure what the right thing to do is for non-DRD
>> mode controllers.
>> ---
>>  drivers/usb/dwc3/core.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index b6a6b90eb2d5..71f8b07ecb99 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -40,6 +40,8 @@
>>  
>>  #define DWC3_DEFAULT_AUTOSUSPEND_DELAY	5000 /* ms */
>>  
>> +static int dwc3_core_soft_reset(struct dwc3 *dwc);
>> +
>>  /**
>>   * dwc3_get_dr_mode - Validates and sets dr_mode
>>   * @dwc: pointer to our context structure
>> @@ -177,6 +179,7 @@ static void __dwc3_set_mode(struct work_struct *work)
>>  
>>  	dwc3_set_prtcap(dwc, dwc->desired_dr_role);
>>  
>> +	dwc3_core_soft_reset(dwc);
> Hi John/Thinh/Felipe,
>
> I actually added this change into my local branch, because we were
> seeing an issue when switching from host mode --> peripheral mode.  What
> was happening was that the RXFIFO register did not update back to the
> expected value for peripheral mode by the time
> dwc3_gadget_init_out_endpoint() was executed.  With the logic to
> calculate the EP max packet limit based on RXFIFO reg, this caused all
> EPs to be set with an EP max limit of 0.
>
> With this change, it seemed to help with the above issue.  However, can
> we consider moving the core soft reset outside the spinlock?  At least
> with our PHY init routines, we have some msleep() calls for waiting for
> the PHYs to be ready, which will end up as a sleeping while atomic bug.
> (not sure if PHY init is required to be called in atomic context)
>
> Thanks
> Wesley Cheng

Hi Wesley,

Thanks for letting us know the issue you're having also.

Yes, you need to wait a certain amount of time to synchronize with the
PHY (at least 50ms for dwc_usb32 and dwc_usb31 v1.80a and above, and
less for older versions). When removing the spinlock to use msleep(),
just make sure that there's no race issue. BTW, how long does your setup
need to msleep()?

As we suggested and explained before, this change is required as part of
the programming guide. It should be added to the driver. It's not a quirk.

BR,
Thinh