This patch adds some in-code documentation to the DSCR related
code to make it more readable without having any functional
change to it.
Signed-off-by: Anshuman Khandual <khand...@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/processor.h | 8 ++++++++
arch/powerpc/kernel/sysfs.c | 13 +++++++++++++
2 files changed, 21 insertions(+)
diff --git a/arch/powerpc/include/asm/processor.h
b/arch/powerpc/include/asm/processor.h
index dda7ac4..81c1aeb 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -295,6 +295,14 @@ struct thread_struct {
#endif
#ifdef CONFIG_PPC64
unsigned long dscr;
+ /*
+ * XXX: dscr_inherit indicates that the process has explicitly
+ * attempted and changed the DSCR register value for itself.
+ * Hence kernel wont use the default CPU DSCR value contained
+ * in the PACA structure anymore during process context switch.
+ * Once this variable is set, this behaviour will be inherited
+ * to all the children of this process from that point onwards.
+ */
int dscr_inherit;
unsigned long ppr; /* used to save/restore SMT priority */
#endif
diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 67fd2fd..edde3f0 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -496,8 +496,21 @@ static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
static DEVICE_ATTR(pir, 0400, show_pir, NULL);
+/*
+ * XXX: This is the system wide DSCR register default value.
+ * Any change to this value through the sysfs interface will
+ * update all per-cpu DSCR default values across the system
+ * stored in their respective PACA structures.
+ */
static unsigned long dscr_default;
+/*
+ * XXX: read_dscr and write_dscr are the functions for the
+ * per-cpu DSCR default sysfs files present for each cpu.
+ * Though updates to per-cpu DSCR value also gets called
+ * for all the CPUs on the system when the system wide
+ * global dscr_default gets changed.
+ */
static void read_dscr(void *val)
{
*(unsigned long *)val = get_paca()->dscr_default;
--
1.9.3
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