x86, cpufreq: fix Speedfreq-SMI call that clobbers ECX

I have found that using SMI to change the cpu's frequency on my DELL
Latitude L400 clobbers the ECX register in speedstep_set_state, causing
unneccessary retries because the "state" variable has changed silently (GCC
assumes it is still present in ECX).

play safe and avoid gcc caching any register across IO port accesses
that trigger SMIs.

Signed-off by: <Stephan.Diestelhorst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 24 insertions, 15 deletions

diff --git a/arch/x86/kernel/cpu/cpufreq/speedstep-smi.c b/arch/x86/kernel/cpu/cpufreq/speedstep-smi.c
index f2b5a621d27b..8a85c93bd62a 100644
--- a/arch/x86/kernel/cpu/cpufreq/speedstep-smi.c
+++ b/arch/x86/kernel/cpu/cpufreq/speedstep-smi.c
@@ -63,7 +63,7 @@ static struct cpufreq_frequency_table speedstep_freqs[] = {
  */
 static int speedstep_smi_ownership (void)
 {
-        u32 command, result, magic;
+        u32 command, result, magic, dummy;
         u32 function = GET_SPEEDSTEP_OWNER;
         unsigned char magic_data[] = "Copyright (c) 1999 Intel Corporation";
 
@@ -73,8 +73,11 @@ static int speedstep_smi_ownership (void)
         dprintk("trying to obtain ownership with command %x at port %x\n", command, smi_port);
 
         __asm__ __volatile__(
+                "push %%ebp\n"
                 "out %%al, (%%dx)\n"
-                : "=D" (result)
+                "pop %%ebp\n"
+                : "=D" (result), "=a" (dummy), "=b" (dummy), "=c" (dummy), "=d" (dummy),
+                        "=S" (dummy)
                 : "a" (command), "b" (function), "c" (0), "d" (smi_port),
                         "D" (0), "S" (magic)
                 : "memory"
@@ -96,7 +99,7 @@ static int speedstep_smi_ownership (void)
  */
 static int speedstep_smi_get_freqs (unsigned int *low, unsigned int *high)
 {
-        u32 command, result = 0, edi, high_mhz, low_mhz;
+        u32 command, result = 0, edi, high_mhz, low_mhz, dummy;
         u32 state=0;
         u32 function = GET_SPEEDSTEP_FREQS;
 
@@ -109,10 +112,12 @@ static int speedstep_smi_get_freqs (unsigned int *low, unsigned int *high)
 
         dprintk("trying to determine frequencies with command %x at port %x\n", command, smi_port);
 
-        __asm__ __volatile__("movl $0, %%edi\n"
+        __asm__ __volatile__(
+                "push %%ebp\n"
                 "out %%al, (%%dx)\n"
-                : "=a" (result), "=b" (high_mhz), "=c" (low_mhz), "=d" (state), "=D" (edi)
-                : "a" (command), "b" (function), "c" (state), "d" (smi_port), "S" (0)
+                "pop %%ebp"
+                : "=a" (result), "=b" (high_mhz), "=c" (low_mhz), "=d" (state), "=D" (edi), "=S" (dummy)
+                : "a" (command), "b" (function), "c" (state), "d" (smi_port), "S" (0), "D" (0)
         );
 
         dprintk("result %x, low_freq %u, high_freq %u\n", result, low_mhz, high_mhz);
@@ -135,16 +140,18 @@ static int speedstep_smi_get_freqs (unsigned int *low, unsigned int *high)
 static int speedstep_get_state (void)
 {
         u32 function=GET_SPEEDSTEP_STATE;
-        u32 result, state, edi, command;
+        u32 result, state, edi, command, dummy;
 
         command = (smi_sig & 0xffffff00) | (smi_cmd & 0xff);
 
         dprintk("trying to determine current setting with command %x at port %x\n", command, smi_port);
 
-        __asm__ __volatile__("movl $0, %%edi\n"
+        __asm__ __volatile__(
+                "push %%ebp\n"
                 "out %%al, (%%dx)\n"
-                : "=a" (result), "=b" (state), "=D" (edi)
-                : "a" (command), "b" (function), "c" (0), "d" (smi_port), "S" (0)
+                "pop %%ebp\n"
+                : "=a" (result), "=b" (state), "=D" (edi), "=c" (dummy), "=d" (dummy), "=S" (dummy)
+                : "a" (command), "b" (function), "c" (0), "d" (smi_port), "S" (0), "D" (0)
         );
 
         dprintk("state is %x, result is %x\n", state, result);
@@ -160,7 +167,7 @@ static int speedstep_get_state (void)
  */
 static void speedstep_set_state (unsigned int state)
 {
-        unsigned int result = 0, command, new_state;
+        unsigned int result = 0, command, new_state, dummy;
         unsigned long flags;
         unsigned int function=SET_SPEEDSTEP_STATE;
         unsigned int retry = 0;
@@ -182,10 +189,12 @@ static void speedstep_set_state (unsigned int state)
                 }
                 retry++;
                 __asm__ __volatile__(
-                        "movl $0, %%edi\n"
+                        "push %%ebp\n"
                         "out %%al, (%%dx)\n"
-                        : "=b" (new_state), "=D" (result)
-                        : "a" (command), "b" (function), "c" (state), "d" (smi_port), "S" (0)
+                        "pop %%ebp"
+                        : "=b" (new_state), "=D" (result), "=c" (dummy), "=a" (dummy),
+                                "=d" (dummy), "=S" (dummy)
+                        : "a" (command), "b" (function), "c" (state), "d" (smi_port), "S" (0), "D" (0)
                         );
         } while ((new_state != state) && (retry <= SMI_TRIES));
 
@@ -195,7 +204,7 @@ static void speedstep_set_state (unsigned int state)
         if (new_state == state) {
                 dprintk("change to %u MHz succeeded after %u tries with result %u\n", (speedstep_freqs[new_state].frequency / 1000), retry, result);
         } else {
-                printk(KERN_ERR "cpufreq: change failed with new_state %u and result %u\n", new_state, result);
+                printk(KERN_ERR "cpufreq: change to state %u failed with new_state %u and result %u\n", state, new_state, result);
         }
 
         return;