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

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Date:   Thu, 1 Jun 2017 14:25:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        tglx@...utronix.de, linux-usb@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability

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.