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

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Message-ID: <20250904000003.b4j7fnucronjf6ej@synopsys.com>
Date: Thu, 4 Sep 2025 00:00:12 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Prashanth K <prashanth.k@....qualcomm.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Log dwc3 instance name in traces

On Wed, Sep 03, 2025, Prashanth K wrote:
> 
> 
> On 9/3/2025 5:14 AM, Thinh Nguyen wrote:
> > On Mon, Sep 01, 2025, Prashanth K wrote:
> >>
> >>
> >> On 8/29/2025 4:18 AM, Thinh Nguyen wrote:
> >>> Hi,
> >>>
> >>> On Mon, Aug 25, 2025, 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 device name to trace events to clearly identify the
> >>>> source instance.
> >>>
> >>> Can we print the base address instead of the device name? This will be
> >>> consistent across different device names, and it will be easier to
> >>> create filter.
> >>>
> >> Did you mean to print the iomem (base address) directly?
> >> I think using device name is more readable, in most cases device name
> >> would contain the base address also. Let me know if you are pointing to
> >> something else.>>
> > 
> > Yes, I mean the device base address. PCI devices won't have the base
> > address as part of the device name.
> > 
> But the base address (void __iomem *base) wouldn't be helpful.
> Using the base address, i guess we would be able to differentiate the
> traces when there are multiple instances, but it wouldn't help us
> identify which controller instance generated which trace.
> 
> And for PCI devices, i agree that it doesn't have  address in device
> name, but i think we should be able to identify the correct instance
> based on the bus/device numbers, right ?
> 

We may not have the PCI domain numbers if it's a child device as in the
case of dwc3-pci or dwc3-haps.

The base address _does_ tell you exactly which device the tracepoints
correspond to. The device name is inconsistent between different device
types and only relevant if we have access to the system to know which
name belongs to which instance.

Also, we (software engineers) are not the only consumer of this. The
the hardware team may also analyze these tracepoints. I'd think more
people are familiar with the base address rather than the naming
convention of the Linux devices.

> >>>> Example trace output,
> >>>> before ->  dwc3_event: event (00000101): Reset [U0]
> >>>> after  ->  dwc3_event: a600000.usb: event (00000101): Reset [U0]
> >>>>
> >>>> Signed-off-by: Prashanth K <prashanth.k@....qualcomm.com>
> 

BR,
Thinh