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

[Selvarasu Ganesan]

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);
+
         ret = dwc3_core_soft_reset(dwc);
         if (ret)
                 goto err_exit_phy;
--
2.34.1

Thanks,
Selva