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Subject[PATCH V3 04/13] powerpc, dscr: Added some in-code documentation
Date
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 <khandual@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/processor.h | 9 +++++++++
arch/powerpc/kernel/sysfs.c | 38 ++++++++++++++++++++++++++++++++++++
2 files changed, 47 insertions(+)

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index bf117d8..28ded5d 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -295,6 +295,15 @@ struct thread_struct {
#endif
#ifdef CONFIG_PPC64
unsigned long dscr;
+ /*
+ * This member element 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 also 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 fa1fd8a..692873b 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -496,13 +496,34 @@ 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);

+/*
+ * This is the system wide DSCR register default value. Any
+ * change to this default 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;

+/**
+ * read_dscr() - Fetch the cpu specific DSCR default
+ * @val: Returned cpu specific DSCR default value
+ *
+ * This function returns the per cpu DSCR default value
+ * for any cpu which is contained in it's PACA structure.
+ */
static void read_dscr(void *val)
{
*(unsigned long *)val = get_paca()->dscr_default;
}

+
+/**
+ * write_dscr() - Update the cpu specific DSCR default
+ * @val: New cpu specific DSCR default value to update
+ *
+ * This function updates the per cpu DSCR default value
+ * for any cpu which is contained in it's PACA structure.
+ */
static void write_dscr(void *val)
{
get_paca()->dscr_default = *(unsigned long *)val;
@@ -520,12 +541,29 @@ static void add_write_permission_dev_attr(struct device_attribute *attr)
attr->attr.mode |= 0200;
}

+/**
+ * show_dscr_default() - Fetch the system wide DSCR default
+ * @dev: Device structure
+ * @attr: Device attribute structure
+ * @buf: Interface buffer
+ *
+ * This function returns the system wide DSCR default value.
+ */
static ssize_t show_dscr_default(struct device *dev,
struct device_attribute *attr, char *buf)
{
return sprintf(buf, "%lx\n", dscr_default);
}

+/**
+ * store_dscr_default() - Update the system wide DSCR default
+ * @dev: Device structure
+ * @attr: Device attribute structure
+ * @buf: Interface buffer
+ * @count: Size of the update
+ *
+ * This function updates the system wide DSCR default value.
+ */
static ssize_t __used store_dscr_default(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
--
1.9.3


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