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

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Message-ID: <20260114225441.rn3affmwuhfl2z7x@synopsys.com>
Date: Wed, 14 Jan 2026 22:54:48 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Prashanth K <prashanth.k@....qualcomm.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "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 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.

BR,
Thinh