linux-kernel - Re: [PATCH v4 3/3] usb: dwc3: Log dwc3 address in traces

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Message-ID: <26f7cb41-5fa0-4aca-a119-2a7510b027a0@oss.qualcomm.com>
Date: Fri, 16 Jan 2026 11:07:52 +0530
From: Prashanth K <prashanth.k@....qualcomm.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] usb: dwc3: Log dwc3 address in traces



On 1/15/2026 9:52 PM, Thinh Nguyen wrote:
> On Thu, Jan 15, 2026, Greg Kroah-Hartman wrote:
>> On Wed, Jan 14, 2026 at 11:54:03PM +0000, Thinh Nguyen wrote:
>>> On Wed, Jan 14, 2026, Thinh Nguyen wrote:
>>>> On Wed, Jan 14, 2026, Greg Kroah-Hartman wrote:
>>>>> On Wed, Jan 14, 2026 at 03:37:48PM +0530, Prashanth K wrote:
>>>>>> + * @address: Cached lower 32-bit base address to be used for logging.
>>>>>
>>>>> Why are 32bits enough / ok?  Why not use the full 64 that you really
>>>>> have?  What happens if you have 2 devices with just the upper 32 bits
>>>>> different?
>>>>>
>>>>> This is a resource value, so why not use the proper type for it?
>>>>>
>>>>
>>>> This is only intented to be used for logging, so I suggested to use u32.
>>>> I want to avoid treating this struct member as a phys_addr_t where it
>>>> may be misused.
>>>>
>>>> As for the reason to capture only the lower 32-bit, it's just base on
>>>> what I've seen so far. That I have not seen designs where the 2 or more
>>>> instances are placed that far apart and share the same lower 32-bit.
>>>> It's a bit nicer to shorten the address print at the start of a
>>>> tracepoint. But if it's insufficient, there's no problem with using
>>>> 64-bit.
>>>>
>>>
>>> Or we can just remove this and print the address from
>>> dwc->xhci_resources[0].start.
>>
>> I thought I asked for that a few revisions ago :)
> 
> Ah, I missed that.
> 
>>
>> I'd prefer that, instead of saving off a value that you can look up if
>> you need it.
>>
> 
> Yes, this is better.
> 
> Hi Prashanth, can we just use dwc->xhci_resources[0].start instead?
> 

While its true that we can avoid adding new variable into dwc3 struct,
using 'xhci_resources[0].start' in DWC3 core traces can be confusing for
someones reading code, since all of the traces are related to dwc3 core
and gadget.

Regards,
Prashanth K