Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability

From	Steven Rostedt <rostedt@goodmis.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability
Date	2017-06-02 02:50 +0200
Message-ID	<tNIWR-1Hb-3@gated-at.bofh.it> (permalink)
References	(3 earlier) <tN2uB-7Lw-1@gated-at.bofh.it> <tN8gF-2XV-1@gated-at.bofh.it> <tNp7P-5BO-7@gated-at.bofh.it> <tNtuO-61-29@gated-at.bofh.it> <tNxoK-2tN-23@gated-at.bofh.it>
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On Thu, 1 Jun 2017 14:25:51 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Jun 01, 2017 at 10:15:24AM +0200, Vlastimil Babka wrote:
> > Thanks. I didn't make it clear that the trace_printk() warning is
> > there even if the code using it doesn't actually execute (i.e. I
> > didn't specify any early_printk bootparam). There are some roastedy
> > tricks to detect the potential users, so that the buffers can be
> > allocated in advance to allow the first trace_printk() from any
> > context, I guess.
> > 
> > I'm not sure if there's a way to change it so that your driver
> > reports the trace_printk usage only in response to the bootparam
> > (which could also be a safe point to allocate ftrace buffers?).  
> 
> No, nor do we want to. There should not be a single caller to
> trace_printk() in normal kernels.

Correct. If you find a trace_printk() that would be useful in a
production environment, then make it a tracepoint.

That's why I have that nasty banner, to make sure trace_printk()s are
not the "quick way" to add tracepoint hacks.

-- Steve

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Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Vlastimil Babka <vbabka.lkml@gmail.com> - 2017-05-30 15:50 +0200
  Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Lu Baolu <baolu.lu@linux.intel.com> - 2017-05-31 05:30 +0200
    Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Steven Rostedt <rostedt@goodmis.org> - 2017-05-31 08:30 +0200
      Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Lu Baolu <baolu.lu@linux.intel.com> - 2017-06-01 05:40 +0200
    Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Vlastimil Babka <vbabka@suse.cz> - 2017-05-31 11:40 +0200
      Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Lu Baolu <baolu.lu@linux.intel.com> - 2017-06-01 05:40 +0200
        Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Vlastimil Babka <vbabka@suse.cz> - 2017-06-01 10:20 +0200
          Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Peter Zijlstra <peterz@infradead.org> - 2017-06-01 14:30 +0200
            Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability Steven Rostedt <rostedt@goodmis.org> - 2017-06-02 02:50 +0200

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