[PATCH v2 1/8] power: supply: Pack power_supply_desc to eliminate holes

[Waqar Hameed]

`pahole` reports that there are two holes in `struct power_supply_desc`:

  struct power_supply_desc {
          const char  *              name;                 /*     0     4 */
          enum power_supply_type     type;                 /*     4     4 */
          u8                         charge_behaviours;    /*     8     1 */

          /* XXX 3 bytes hole, try to pack */

          u32                        charge_types;         /*    12     4 */
          u32                        usb_types;            /*    16     4 */
          const enum power_supply_property  * properties;  /*    20     4 */
          size_t                     num_properties;       /*    24     4 */
          int                        (*get_property)(...); /*    28     4 */
          int                        (*set_property)(...); /*    32     4 */
          int                        (*property_is_writeable)(...);  /*    36     4 */
          void                       (*external_power_changed)(...); /*    40     4 */
          int                        (*init)(struct power_supply *); /*    44     4 */
          bool                       no_thermal;           /*    48     1 */

          /* XXX 3 bytes hole, try to pack */

          int                        use_for_apm;          /*    52     4 */

          /* size: 56, cachelines: 1, members: 14 */
          /* sum members: 50, holes: 2, sum holes: 6 */
          /* last cacheline: 56 bytes */
  };

This can be optimized by moving `u8 charge_behaviours` to the end and
swapping `int use_for_apm` with `bool no_thermal`:

  struct power_supply_desc {
          const char  *              name;                 /*     0     4 */
          enum power_supply_type     type;                 /*     4     4 */
          u32                        charge_types;         /*     8     4 */
          u32                        usb_types;            /*    12     4 */
          const enum power_supply_property  * properties;  /*    16     4 */
          size_t                     num_properties;       /*    20     4 */
          int                        (*get_property)(...); /*    24     4 */
          int                        (*set_property)(...); /*    28     4 */
          int                        (*property_is_writeable)(...);  /*    32     4 */
          void                       (*external_power_changed)(...); /*    36     4 */
          int                        (*init)(struct power_supply *); /*    40     4 */
          int                        use_for_apm;          /*    44     4 */
          bool                       no_thermal;           /*    48     1 */
          u8                         charge_behaviours;    /*    49     1 */

          /* size: 52, cachelines: 1, members: 14 */
          /* padding: 2 */
          /* last cacheline: 52 bytes */
  };

Do this in order to save 4 bytes. This will also help when adding new
members in the future to this `struct`.

Signed-off-by: Waqar Hameed <waqar.hameed@xxxxxxxx>
---
 include/linux/power_supply.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index e749d21893352..fcd05f4a88833 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -259,7 +259,6 @@ struct power_supply_config {
 struct power_supply_desc {
 	const char *name;
 	enum power_supply_type type;
-	u8 charge_behaviours;
 	u32 charge_types;
 	u32 usb_types;
 	const enum power_supply_property *properties;
@@ -295,14 +294,17 @@ struct power_supply_desc {
 	 */
 	int (*init)(struct power_supply *psy);
 
+	/* For APM emulation, think legacy userspace. */
+	int use_for_apm;
+
 	/*
 	 * Set if thermal zone should not be created for this power supply.
 	 * For example for virtual supplies forwarding calls to actual
 	 * sensors or other supplies.
 	 */
 	bool no_thermal;
-	/* For APM emulation, think legacy userspace. */
-	int use_for_apm;
+
+	u8 charge_behaviours;
 };
 
 struct power_supply_ext {
-- 
2.43.0