linux-kernel - ehci dynamic debug problem

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Date:	Fri, 13 Apr 2012 10:56:07 +0200
From:	Johannes Stezenbach <js@...21.net>
To:	Jason Baron <jbaron@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	linux-usb@...r.kernel.org
Subject: ehci dynamic debug problem

Hi,

I have a quirky device and enabled dynamic debug to
see the ehci driver debug messages to help me diagnose
the problem.  I see stuff like this:

[1790542.363321] ehci_hub_control:940: ehci_hcd 0000:00:1a.0: \xffffffd8\xffffff94\xffffff94\xffffffa8\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff}[<\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff\x01
[1790542.363470] ehci_hub_control:940: ehci_hcd 0000:00:1a.0: \xffffffd8\xffffff94\xffffff94\xffffffa8\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff}[<\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff\x01

The problem is in ehci-dbg.c:

#define dbg_port(ehci, label, port, status) { \
	char _buf [80]; \
	dbg_port_buf (_buf, sizeof _buf, label, port, status); \
	ehci_dbg (ehci, "%s\n", _buf); \
}

dbg_port_buf() is a no op when DEBUG is not defined, thus
the ehci_dbg() prints uninitialized memory.

Does dynamic debug offer an "is the message two lines below enabled" test?
Simply changing the "#ifdef DEBUG" for dbg_port_buf()
to "#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)"
is probably not acceptable due to the overhead of dbg_port_buf()?

Thanks,
Johannes
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