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

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Message-ID: <20250904234409.etyz6ep3y4rfr3he@synopsys.com>
Date: Thu, 4 Sep 2025 23:44:16 +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 Thu, Sep 04, 2025, Prashanth K wrote:
> 
> 
> On 9/4/2025 5:30 AM, Thinh Nguyen wrote:
> > 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.
> 
> Yes, I agree that device name would be inconsistent for different for
> PCI (and HAPS) devices. But IMO using base address (virtual) would just
> make it more harder to read and identify the instance.
> 
> Perhaps we can cache the register addr and use it, what do you think?
> Here we can at least differentiate the instances based on HW addr.
> 
> snprintf(dwc->inst, sizeof(dwc->inst), "0x%08llx", (unsigned long
> long)res->start);
> dev_info(dwc->dev, "addr:%s\n", dwc->inst);
> 
> Output --> [    4.521746] dwc3 a600000.usb: addr:0x0a600000

I think there's some misunderstanding here. I refer the base address as
the hardware address.

I prefer something like this:

    dwc3_event: 0a600000: event (00000101): Reset [U0]

instead of the device name like this:

   dwc3_event: a600000.usb: event (00000101): Reset [U0]

BR,
Thinh