Re: [PATCH] usb: dwc3: Fix GUID register programming order

[Selvarasu Ganesan]

On 4/17/2026 3:54 AM, Thinh Nguyen wrote:
> On Wed, Apr 15, 2026, Selvarasu Ganesan wrote:
>> On 4/15/2026 7:16 AM, Thinh Nguyen wrote:
>>> On Tue, Apr 14, 2026, Selvarasu Ganesan wrote:
>>>> On 4/14/2026 6:35 AM, Thinh Nguyen wrote:
>>>>> On Fri, Apr 10, 2026, Selvarasu Ganesan wrote:
>>>>>> The Linux Version Code is currently written to the GUID register before
>>>>>> dwc3_core_soft_reset() is executed. Since the core soft reset clears the
>>>>>> GUID register back to its default value, the version information is
>>>>>> subsequently lost.
>>>>> This is not right. Soft reset should not clear the GUID register.
>>>>> Something else must have cleared it. Did you assert Vcc reset (hard
>>>>> reset) during phy reset/initialization?
>>>>>
>>>>> BR,
>>>>> Thinh
>>>> Hi Thinh,
>>>>
>>>> Thank you for the clarification. Yes, you are correct, this issue is not
>>>> related to a dwc3 core soft reset. Instead, the GUID value reverts to
>>>> its default state when the PHY link_sw_reset completes during PHY init
>>>> sequence.
>>>>
>>>> We are using the Synopsys eUSB PHY, this reset is triggered from our
>>>> downstream driver during the PHY init sequence (invoked through
>>>> |dwc3_core_init|).
>>>>
>>>> Could you please suggest the best way to retrieve the correct linux
>>>> version information from the GUID?
>>>> Additionally, would it be feasible to update the GUID register after the
>>>> PHY init sequence (triggered by |dwc3_core_init|) completes?
>>>>
>>> Yes. Just fix up the changelog to properly describe the problem and
>>> solution.
>>>
>>> BR,
>>> Thinh
>> Hi Thinh,
>>
>> Thanks for the confirmation. I have modified the changelog as shown
>> below, please review it once then i will post updated patchset.
>>
>>
>> From: Selvarasu Ganesan <selvarasu.g@xxxxxxxxxxx>
>> Date: Thu, 9 Apr 2026 18:34:03 +0530
>> Subject: [PATCH v2] usb: dwc3: Move GUID programming after PHY
>> initialization
>>
>> The Linux Version Code is currently written to the GUID register before
>> PHY initialization. Certain PHY implementations (such as Synopsys eUSB
>> PHY performing link_sw_reset) clear the GUID register to its default
>> value during initialization, causing the kernel version information to
>> be lost.
>>
>> Move the GUID register programming to occur after PHY initialization
>> completes to ensure the Linux version information persists.
>>
>> Fixes: fa0ea13e9f1c ("usb: dwc3: core: write LINUX_VERSION_CODE to our
>> GUID register")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Reported-by: Pritam Manohar Sutar <pritam.sutar@xxxxxxxxxxx>
>> Signed-off-by: Selvarasu Ganesan <selvarasu.g@xxxxxxxxxxx>
>> ---
>>    drivers/usb/dwc3/core.c | 12 ++++++------
>>    1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 161a4d58b2cec..8b9e9d3e9589a 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -1341,12 +1341,6 @@ int dwc3_core_init(struct dwc3 *dwc)
>>
>>           hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
>>
>> -       /*
>> -        * Write Linux Version Code to our GUID register so it's easy to
>> figure
>> -        * out which kernel version a bug was found.
>> -        */
>> -       dwc3_writel(dwc, DWC3_GUID, LINUX_VERSION_CODE);
>> -
>>           ret = dwc3_phy_setup(dwc);
>>           if (ret)
>>                   return ret;
>> @@ -1374,6 +1368,12 @@ int dwc3_core_init(struct dwc3 *dwc)
>>           if (ret)
>>                   goto err_exit_ulpi;
>>
>> +       /*
>> +        * Write Linux Version Code to our GUID register so it's easy to
>> figure
>> +        * out which kernel version a bug was found.
>> +        */
>> +       dwc3_writel(dwc, DWC3_GUID, LINUX_VERSION_CODE);
>> +
> In the really old kernel, the phy init was part of the
> dwc3_core_soft_reset(). Move this after dwc3_core_soft_reset() just as
> you had before. It will be better for backporting, and it looks more
> fitting to place it there.

Sure.

>
>>           ret = dwc3_core_soft_reset(dwc);
>>           if (ret)
>>                   goto err_exit_phy;
>
> The changelog looks good.

Ok. Thanks for the confirmation.

Thanks,
Selva

>
> Thanks,
> Thinh