[CPUFREQ] SPEEDSTEP_RELAXED_CAP_CHECK option.

A few SpeedStep-capable systems don't perform according to specification: the
CPUID and/or some MSRs don't tell us the CPU is SpeedStep capable even though
it definitely is. Allow a relaxed checking for one such issue by a module
parameter only available if a config option is turned on. This is done to
avoid the risk of doing invalid speedstep instructions on systems which do
not support it, and which might even lead to (hardware) failure.
                                                                                                   
Patch originally from Andres Aeriksson (?) aeriksson at fastmail (dot) fm

arch/i386/kernel/cpu/cpufreq/Kconfig

@@ -176,6 +176,16 @@ config X86_SPEEDSTEP_LIB
 	depends on (X86_SPEEDSTEP_ICH || X86_SPEEDSTEP_SMI || X86_P4_CLOCKMOD)
 	default (X86_SPEEDSTEP_ICH || X86_SPEEDSTEP_SMI || X86_P4_CLOCKMOD)
 
+config X86_SPEEDSTEP_RELAXED_CAP_CHECK
+	bool "Relaxed speedstep capability checks"
+	depends on (X86_SPEEDSTEP_SMI || X86_SPEEDSTEP_ICH)
+	help
+	  Don't perform all checks for a speedstep capable system which would 
+	  normally be done. Some ancient or strange systems, though speedstep 
+	  capable, don't always indicate that they are speedstep capable. This 
+	  option let's the probing code bypass some of those checks if the
+	  parameter "relaxed_check=1" is passed to the module.
+
 config X86_LONGRUN
 	tristate "Transmeta LongRun"
 	depends on CPU_FREQ

arch/i386/kernel/cpu/cpufreq/speedstep-lib.c

@@ -10,6 +10,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h> 
+#include <linux/moduleparam.h>
 #include <linux/init.h>
 #include <linux/cpufreq.h>
 #include <linux/pci.h>
@@ -30,6 +31,12 @@
 #define dprintk(msg...) do { } while(0)
 #endif
 
+#ifdef CONFIG_X86_SPEEDSTEP_RELAXED_CAP_CHECK
+static int relaxed_check = 0;
+#else
+#define relaxed_check 0
+#endif
+
 /*********************************************************************
  *                   GET PROCESSOR CORE SPEED IN KHZ                 *
  *********************************************************************/
@@ -265,6 +272,7 @@ unsigned int speedstep_detect_processor (void)
 		ebx = cpuid_ebx(0x00000001);
 
 		ebx &= 0x000000FF;
+
 		if (ebx != 0x06)
 			return 0;
 
@@ -292,7 +300,7 @@ unsigned int speedstep_detect_processor (void)
 		 */
 		rdmsr(MSR_IA32_PLATFORM_ID, msr_lo, msr_hi);
 		dprintk(KERN_DEBUG "cpufreq: Coppermine: MSR_IA32_PLATFORM ID is 0x%x, 0x%x\n", msr_lo, msr_hi);
-		if ((msr_hi & (1<<18)) && (msr_hi & (3<<24))) {
+		if ((msr_hi & (1<<18)) && (relaxed_check ? 1 : (msr_hi & (3<<24)))) {
 			if (c->x86_mask == 0x01)
 				return SPEEDSTEP_PROCESSOR_PIII_C_EARLY;
 			else
@@ -362,6 +370,11 @@ unsigned int speedstep_get_freqs(unsigned int processor,
 }
 EXPORT_SYMBOL_GPL(speedstep_get_freqs);
 
+#ifdef CONFIG_X86_SPEEDSTEP_RELAXED_CAP_CHECK
+module_param(relaxed_check, int, 0444);
+MODULE_PARM_DESC(relaxed_check, "Don't do all checks for speedstep capability.");
+#endif
+
 MODULE_AUTHOR ("Dominik Brodowski <linux@brodo.de>");
 MODULE_DESCRIPTION ("Library for Intel SpeedStep 1 or 2 cpufreq drivers.");
 MODULE_LICENSE ("GPL");