[PATCH] pwm: cros_ec: add __packed to prevent padding

From: Brian Norris
Date: Tue Jul 26 2016 - 14:22:46 EST

While the particular usage in question is likely safe (struct
cros_ec_command is 32-bit aligned, followed by <=32-bit fields), it's
been suggested this is not a great pattern to follow for the general
case -- for example, if we follow a 'struct cros_ec_command' (which is
32-bit- but not 64-bit-aligned) with a struct that starts with a 64-bit
type (e.g., u64), the compiler may add padding.

Let's add __packed, to inform the compiler of our true intention -- to
have no padding between these struct elements -- and to future proof for
any refactorings that might occur.

Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
Hi Thierry,

I don't know of any bugs directly resolved by this patch, so take it for
v4.8/v4.9 at your discretion.

drivers/pwm/pwm-cros-ec.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-cros-ec.c b/drivers/pwm/pwm-cros-ec.c
index 99b9acc1a420..f6ca4e8c6253 100644
--- a/drivers/pwm/pwm-cros-ec.c
+++ b/drivers/pwm/pwm-cros-ec.c
@@ -38,7 +38,7 @@ static int cros_ec_pwm_set_duty(struct cros_ec_device *ec, u8 index, u16 duty)
struct {
struct cros_ec_command msg;
struct ec_params_pwm_set_duty params;
- } buf;
+ } __packed buf;
struct ec_params_pwm_set_duty *params = &buf.params;
struct cros_ec_command *msg = &buf.msg;

@@ -65,7 +65,7 @@ static int __cros_ec_pwm_get_duty(struct cros_ec_device *ec, u8 index,
struct ec_params_pwm_get_duty params;
struct ec_response_pwm_get_duty resp;
- } buf;
+ } __packed buf;
struct ec_params_pwm_get_duty *params = &buf.params;
struct ec_response_pwm_get_duty *resp = &buf.resp;
struct cros_ec_command *msg = &buf.msg;