title: enable linux kernel driver dev_dbg debug messages
body: <p>is there a simplest possible way to enable linux kernel driver <code>dev_dbg</code> debug messages (actually it's a <code>trace</code> style messages) hopefully without messing up with the kernel patching/recompiling or the driver implementing something extra like <code>debugfs</code>? perhaps there is a way to enable something SIMPLE in the kernel (like one flag?) triggering particular driver or all drivers dev_dbg (it can be filtered with the `dmesg|grep "driverName") output?</p>
  
  <p>the kernel version is <code>4.14</code>.
  there is NO <code>syslog/daemonlog/system</code> log running at all. there is NO network interface and only single serial port is available. the target system is very slow and is very compact so there is NO WAY to add syslog/etc, there is nothing but dmesg where exactly would be good to see the output of the lines like:</p>
  
  <p><code>dev_dbg(&amp;client-&gt;dev, "bla bla bla\n");</code></p>
  
  <p>some posts already suggested to add <code>debug</code> keyword for the <code>bootargs</code> kernel parameters unfortunately wasn't enough.</p>
  
  <p>the outputs like <code>dev_info</code> are getting into the dmesg with no issue so it's definitely something close. thanks</p>