linux-kernel - Re: [PATCH 1/2] usb: dwc3: Add trace event for dwc3_set

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Message-ID: <20250821233035.e2yl3yvoq5i4jpdz@synopsys.com>
Date: Thu, 21 Aug 2025 23:30:36 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Kuen-Han Tsai <khtsai@...gle.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <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 1/2] usb: dwc3: Add trace event for dwc3_set_prtcap

On Mon, Aug 18, 2025, Kuen-Han Tsai wrote:
> Changes to the port capability can be indirectly observed by tracing
> register writes to DWC3_GCTL. However, this requires interpreting the
> raw value, which is neither intuitive nor precise for debugging.
> Monitoring these mode changes is essential for resolving issues related
> to USB role switching and enumeration.
> 
> Introduce a dedicated trace event to provide a human-readable log when
> the port capability is configured.
> 
> Signed-off-by: Kuen-Han Tsai <khtsai@...gle.com>
> ---
>  drivers/usb/dwc3/core.c  |  1 +
>  drivers/usb/dwc3/debug.h | 18 ++++++++++++++++++
>  drivers/usb/dwc3/trace.h | 17 +++++++++++++++++
>  3 files changed, 36 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 8002c23a5a02..370fc524a468 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -156,6 +156,7 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
>  	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
>  
>  	dwc->current_dr_role = mode;
> +	trace_dwc3_set_prtcap(mode);
>  }
>  
>  static void __dwc3_set_mode(struct work_struct *work)
> diff --git a/drivers/usb/dwc3/debug.h b/drivers/usb/dwc3/debug.h
> index 09d703852a92..70d90790f872 100644
> --- a/drivers/usb/dwc3/debug.h
> +++ b/drivers/usb/dwc3/debug.h
> @@ -13,6 +13,24 @@
>  
>  #include "core.h"
>  
> +/**
> + * dwc3_mode_string - returns mode name
> + * @mode: mode code

Minor nit: would be better to document as GCTL.PrtCapDir value, but it's
obvious looking at this small function. So it's fine.

> + */
> +static inline const char *dwc3_mode_string(u32 mode)
> +{
> +	switch (mode) {
> +	case DWC3_GCTL_PRTCAP_HOST:
> +		return "host";
> +	case DWC3_GCTL_PRTCAP_DEVICE:
> +		return "device";
> +	case DWC3_GCTL_PRTCAP_OTG:
> +		return "otg";
> +	default:
> +		return "UNKNOWN";
> +	}
> +}
> +
>  /**
>   * dwc3_gadget_ep_cmd_string - returns endpoint command string
>   * @cmd: command code
> diff --git a/drivers/usb/dwc3/trace.h b/drivers/usb/dwc3/trace.h
> index bdeb1aaf65d8..b6ba984bafcd 100644
> --- a/drivers/usb/dwc3/trace.h
> +++ b/drivers/usb/dwc3/trace.h
> @@ -19,6 +19,23 @@
>  #include "core.h"
>  #include "debug.h"
>  
> +DECLARE_EVENT_CLASS(dwc3_log_set_prtcap,
> +	TP_PROTO(u32 mode),
> +	TP_ARGS(mode),
> +	TP_STRUCT__entry(
> +		__field(u32, mode)
> +	),
> +	TP_fast_assign(
> +		__entry->mode = mode;
> +	),
> +	TP_printk("mode %s", dwc3_mode_string(__entry->mode))
> +);
> +
> +DEFINE_EVENT(dwc3_log_set_prtcap, dwc3_set_prtcap,
> +	TP_PROTO(u32 mode),
> +	TP_ARGS(mode)
> +);
> +
>  DECLARE_EVENT_CLASS(dwc3_log_io,
>  	TP_PROTO(void *base, u32 offset, u32 value),
>  	TP_ARGS(base, offset, value),
> -- 
> 2.51.0.rc1.163.g2494970778-goog
> 

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh