linux-kernel - Re: [PATCH v2 3/3] usb: dwc3: Log dwc3 instance name in traces

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Message-ID: <dec18683-5b43-464f-a735-4bf26644aa0a@oss.qualcomm.com>
Date: Wed, 7 Jan 2026 11:33:11 +0530
From: Prashanth K <prashanth.k@....qualcomm.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] usb: dwc3: Log dwc3 instance name in traces



On 1/6/2026 3:28 PM, Greg Kroah-Hartman wrote:
> On Mon, Jan 05, 2026 at 05:23:25PM +0530, Prashanth K wrote:
>> When multiple DWC3 controllers are being used, trace events from
>> different instances get mixed up making debugging difficult as
>> there's no way to distinguish which instance generated the trace.
>>
>> Append the base address of dwc3 controller to trace events, so that
>> the source instance is clearly identifiable.
>>
>> Example trace output,
>> before ->  dwc3_event: event (00000101): Reset [U0]
>> after  ->  dwc3_event: 0a600000: event (00000101): Reset [U0]
>>
>> Signed-off-by: Prashanth K <prashanth.k@....qualcomm.com>
>> ---
>>  drivers/usb/dwc3/core.c   |  6 ++-
>>  drivers/usb/dwc3/core.h   |  2 +
>>  drivers/usb/dwc3/ep0.c    |  2 +-
>>  drivers/usb/dwc3/gadget.c |  2 +-
>>  drivers/usb/dwc3/io.h     |  4 +-
>>  drivers/usb/dwc3/trace.h  | 88 ++++++++++++++++++++++++---------------
>>  6 files changed, 66 insertions(+), 38 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 670a9d4bfff2..3aa85f5f1c47 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -158,7 +158,7 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
>>  	dwc3_writel(dwc, DWC3_GCTL, reg);
>>  
>>  	dwc->current_dr_role = mode;
>> -	trace_dwc3_set_prtcap(mode);
>> +	trace_dwc3_set_prtcap(dwc, mode);
>>  }
>>  EXPORT_SYMBOL_GPL(dwc3_set_prtcap);
>>  
>> @@ -2193,6 +2193,10 @@ int dwc3_core_probe(const struct dwc3_probe_data *data)
>>  	dwc_res = *res;
>>  	dwc_res.start += DWC3_GLOBALS_REGS_START;
>>  
>> +	/* Store the physical base address for logging in trace */
>> +	snprintf(dwc->base_addr, sizeof(dwc->base_addr), "%08llx",
>> +		 (unsigned long long)res->start);
> 
> I think start is defined as resource_size_t, which is really
> phys_addr_t, which is then either a u64 or u32, so why not just use u64
> here?
> 
Yes, we can substitute u64 instead of `unsigned long long`

+	snprintf(dwc->base_addr, sizeof(dwc->base_addr), "%08llx",
+		 (u64)res->start);

> And are you _sure_ it is ok to expose that to userspace?
> 
yes, because it's already part of devname in most cases.
> 
>> +
>>  	if (dev->of_node) {
>>  		struct device_node *parent = of_get_parent(dev->of_node);
>>  
>> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
>> index 23188b910528..c16e47273ea0 100644
>> --- a/drivers/usb/dwc3/core.h
>> +++ b/drivers/usb/dwc3/core.h
>> @@ -1178,6 +1178,7 @@ struct dwc3_glue_ops {
>>   * @wakeup_pending_funcs: Indicates whether any interface has requested for
>>   *			 function wakeup in bitmap format where bit position
>>   *			 represents interface_id.
>> + * @base_addr: The HW base address of DWC3 controller.
> 
> You already have this pointer to the resource in dwc3 somewhere, so why
> are you storing this as a char string and not just always using the
> "real" resource instead?
> 
No Greg, dwc3 struct doesn't have the resource pointer, but has res for
xhci.

> And also, document this as ONLY needed for debugging things, that's not
> obvious here at all.
> 
Sure

Regards,
Prashanth K