Hi, On 05/30/2017 09:46 PM, Vlastimil Babka wrote: > 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. This feature is only for a DEBUG kernel, should not be enabled for any production kernel. This was the reason I enabled trace_printk() by default. Best regards, Lu Baolu > 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
