Re: ehci dynamic debug problem

Jason Baron
2012-04-16T15:54:34Z

On Fri, Apr 13, 2012 at 09:03:11PM +0200, Johannes Stezenbach wrote:
> On Fri, Apr 13, 2012 at 02:13:58PM -0400, Alan Stern wrote:
> > On Fri, 13 Apr 2012, Johannes Stezenbach wrote:
> >
> > > > But there is no such thing as dynamic debug for ehci, is there?
> > > > There's a separate dynamic debug setting for each dev_dbg statement.
> > > > So your ideal solution makes no sense.
> > >
> > > When CONFIG_DYNAMIC_DEBUG=y but ehci debug is disabled
> >
> > There is no such thing as ehci debug! So how can it be disabled?
> > There's only an individual setting for each line of debugging code.
> >
> > > in /sys/kernel/debug/dynamic_debug/control, then
> > > dbg_port() calls dbg_port_buf() which would
> > > format the string, then calls ehci_dbg() which
> > > calls dev_dbg() which discards it.
> > >
> > > Does it make sense now?
> >
> > No. What happens if dynamic debug is enabled for one line that calls
> > dbg_port_buf() but not for another? There's no way to avoid the string
> > formatting in both lines, even though one of them discards the result.
>
> That's why I said in my initial mail:
>
> Does dynamic debug offer an "is the message two lines below enabled" test?
>

Sorry was away for a bit...

dynamic debug doesn't offer any is enabled test, its hidden from the
user. That said, in this case, you can delay the printing to the buffer
with:

diff --git a/drivers/usb/host/ehci-dbg.c b/drivers/usb/host/ehci-dbg.c
index d6d74d2..fd90ccd 100644
--- a/drivers/usb/host/ehci-dbg.c
+++ b/drivers/usb/host/ehci-dbg.c
@@ -254,7 +255,7 @@ dbg_command_buf (char *buf, unsigned len, const char *label, u32 command)
);
}

-static int
+static char *
dbg_port_buf (char *buf, unsigned len, const char *label, int port, u32 status)
{
char *sig;
@@ -267,7 +268,7 @@ dbg_port_buf (char *buf, unsigned len, const char *label, int port, u32 status)
default: sig = "?"; break;
}

- return scnprintf (buf, len,
+ scnprintf (buf, len,
"%s%sport:%d status %06x %d %s%s%s%s%s%s "
"sig=%s%s%s%s%s%s%s%s%s%s%s",
label, label [0] ? " " : "", port, status,
@@ -293,6 +294,8 @@ dbg_port_buf (char *buf, unsigned len, const char *label, int port, u32 status)
(status & PORT_PE) ? " PE" : "",
(status & PORT_CSC) ? " CSC" : "",
(status & PORT_CONNECT) ? " CONNECT" : "");
+
+ return buf;
}

#else
@@ -333,8 +336,7 @@ dbg_port_buf (char *buf, unsigned len, const char *label, int port, u32 status)

#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); \
+ ehci_dbg (ehci, "%s\n", dbg_port_buf (_buf, sizeof _buf, label, port, status)); \
}

/*-------------------------------------------------------------------------*/

That seems to do what you want, at least with my compiler - gcc (GCC)
4.6.2 20111027 (Red Hat 4.6.2-1).

Thanks,

-Jason