Hi, On 05/31/2017 05:38 PM, Vlastimil Babka wrote: > On 05/31/2017 05:27 AM, Lu Baolu wrote: >> 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. > Hmm, but it seems we generally enable all these early printk > features/drivers in our distro kernels. They are not active without a > early_printk=X bootparam anyway, right? It's much more convenient to > e.g. just tell customer to change a param when debugging something than > to install a debug kernel. So I wouldn't agree that only a DEBUG kernel > should have this compiled in. Okay, I will try to find a fix. Best regards, Lu Baolu > > Thanks, > Vlastimil > >> 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 > -- 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
