On 03/21/2017 09:01 AM, Lu Baolu wrote: > XHCI debug capability (DbC) is an optional but standalone > functionality provided by an xHCI host controller. Software > learns this capability by walking through the extended > capability list of the host. XHCI specification describes > DbC in the section 7.6. > > This patch introduces the code to probe and initialize the > debug capability hardware during early boot. With hardware > initialized, the debug target (system on which this code is > running) will present a debug device through the debug port > (normally the first USB3 port). The debug device is fully > compliant with the USB framework and provides the equivalent > of a very high performance (USB3) full-duplex serial link > between the debug host and target. The DbC functionality is > independent of the xHCI host. There isn't any precondition > from the xHCI host side for the DbC to work. > > One use for this feature is kernel debugging, for example > when your machine crashes very early before the regular > console code is initialized. Other uses include simpler, > lockless logging instead of a full-blown printk console > driver and klogd. > > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> ... > + > +#define XDBC_TRACE > +#ifdef XDBC_TRACE > +#define xdbc_trace trace_printk Did you forget to remove the #define XDBC_TRACE? Enabling this driver brings the "trace_printk() being used. Allocating extra memory. This means that this is a DEBUG kernel and it is unsafe for production use." message in 4.12-rcX dmesg. Thanks, Vlastimil -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
