linux-kernel - RE: [PATCH] usb: dwc3: debugfs: add snapshot to dump requests trbs events

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Message-ID: <A2CA0424C0A6F04399FB9E1CD98E03046D192103@US01WEMBX2.internal.synopsys.com>
Date:	Mon, 28 Apr 2014 19:58:43 +0000
From:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
To:	"balbi@...com" <balbi@...com>,
	Zhuang Jin Can <jin.can.zhuang@...el.com>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: dwc3: debugfs: add snapshot to dump requests trbs
 events

> From: linux-usb-owner@...r.kernel.org [mailto:linux-usb-owner@...r.kernel.org] On Behalf Of Felipe Balbi
> Sent: Monday, April 28, 2014 8:56 AM
> 
> On Mon, Apr 28, 2014 at 04:49:23PM -0400, Zhuang Jin Can wrote:
> > Adds a debugfs file "snapshot" to dump dwc3 requests, trbs and events.

< snip > 

> > +	for (i = 0; i < evt->length; i += 4) {
> > +		event.raw = *(u32 *) (evt->buf + i);
> > +		if (i == evt->lpos) {
> > +			seq_puts(s, "lpos-------|\n");
> > +			seq_puts(s, "           \\\n");
> > +		}
> > +		seq_printf(s, "event[%d]: %08x ", i, event.raw);
> > +
> > +		if (event.type.is_devspec)
> > +			dwc3_dump_dev_event(s, &event.devt);
> > +		else
> > +			dwc3_dump_ep_event(s, &event.depevt);
> > +		seq_puts(s, "\n");
> > +	}
> 
> how well have you tested this ? I'm not entirely sure you should be
> reading the event buffer at any time you want, though I might be wrong.

Just FYI, it is fine to read from the event buffer memory at any time.
But of course, if you happen to read from a location at the same time
the core is writing to it, you may read either the old value or the new,
depending on the timing. So the results might not be 100% reliable.

-- 
Paul

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