powerpc: Per process DSCR + some fixes (try#4)

The DSCR (aka Data Stream Control Register) is supported on some
server PowerPC chips and allow some control over the prefetch
of data streams.

This patch allows the value to be specified per thread by emulating
the corresponding mfspr and mtspr instructions. Children of such
threads inherit the value. Other threads use a default value that
can be specified in sysfs - /sys/devices/system/cpu/dscr_default.

If a thread starts with non default value in the sysfs entry,
all children threads inherit this non default value even if
the sysfs value is changed later.

Signed-off-by: Alexey Kardashevskiy <aik@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index c0d8c2006bf4..f0f2199e64e1 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -182,6 +182,41 @@ static SYSDEV_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
 static SYSDEV_ATTR(spurr, 0600, show_spurr, NULL);
 static SYSDEV_ATTR(dscr, 0600, show_dscr, store_dscr);
 static SYSDEV_ATTR(purr, 0600, show_purr, store_purr);
+
+unsigned long dscr_default = 0;
+EXPORT_SYMBOL(dscr_default);
+
+static ssize_t show_dscr_default(struct sysdev_class *class,
+                struct sysdev_class_attribute *attr, char *buf)
+{
+        return sprintf(buf, "%lx\n", dscr_default);
+}
+
+static ssize_t __used store_dscr_default(struct sysdev_class *class,
+                struct sysdev_class_attribute *attr, const char *buf,
+                size_t count)
+{
+        unsigned long val;
+        int ret = 0;
+        
+        ret = sscanf(buf, "%lx", &val);
+        if (ret != 1)
+                return -EINVAL;
+        dscr_default = val;
+
+        return count;
+}
+
+static SYSDEV_CLASS_ATTR(dscr_default, 0600,
+                show_dscr_default, store_dscr_default);
+
+static void sysfs_create_dscr_default(void)
+{
+        int err = 0;
+        if (cpu_has_feature(CPU_FTR_DSCR))
+                err = sysfs_create_file(&cpu_sysdev_class.kset.kobj,
+                        &attr_dscr_default.attr);
+}
 #endif /* CONFIG_PPC64 */
 
 #ifdef HAS_PPC_PMC_PA6T
@@ -617,6 +652,9 @@ static int __init topology_init(void)
                 if (cpu_online(cpu))
                         register_cpu_online(cpu);
         }
+#ifdef CONFIG_PPC64
+        sysfs_create_dscr_default();
+#endif /* CONFIG_PPC64 */
 
         return 0;
 }