x86, bts: improve help text for BTS config

Improve the help text of the X86_PTRACE_BTS config.
Make X86_DS invisible and depend on X86_PTRACE_BTS.
Reported-by: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/Kconfig.cpu

@@ -513,19 +513,19 @@ config CPU_SUP_UMC_32
 	  If unsure, say N.
 
 config X86_DS
-	bool "Debug Store support"
-	default y
-	help
-	  Add support for Debug Store.
-	  This allows the kernel to provide a memory buffer to the hardware
-	  to store various profiling and tracing events.
+	def_bool X86_PTRACE_BTS
+	depends on X86_DEBUGCTLMSR
 
 config X86_PTRACE_BTS
-	bool "ptrace interface to Branch Trace Store"
+	bool "Branch Trace Store"
 	default y
-	depends on (X86_DS && X86_DEBUGCTLMSR)
+	depends on X86_DEBUGCTLMSR
 	help
-	  Add a ptrace interface to allow collecting an execution trace
-	  of the traced task.
-	  This collects control flow changes in a (cyclic) buffer and allows
-	  debuggers to fill in the gaps and show an execution trace of the debuggee.
+	  This adds a ptrace interface to the hardware's branch trace store.
+
+	  Debuggers may use it to collect an execution trace of the debugged
+	  application in order to answer the question 'how did I get here?'.
+	  Debuggers may trace user mode as well as kernel mode.
+
+	  Say Y unless there is no application development on this machine
+	  and you want to save a small amount of code size.