* Re: [PATCH] pwm: cros_ec: add __packed to prevent padding
2016-07-26 18:22 [PATCH] pwm: cros_ec: add __packed to prevent padding Brian Norris
@ 2016-07-26 19:03 ` Dmitry Torokhov
2016-07-26 20:15 ` Guenter Roeck
2016-09-05 6:44 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Dmitry Torokhov @ 2016-07-26 19:03 UTC (permalink / raw)
To: Brian Norris
Cc: Thierry Reding, linux-kernel, Brian Norris, linux-pwm,
Javier Martinez Canillas, Enric Balletbo, Gwendal Grignou,
Guenter Roeck
On Tue, Jul 26, 2016 at 11:22:13AM -0700, Brian Norris wrote:
> 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@chromium.org>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---
> 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;
> --
> 2.8.0.rc3.226.g39d4020
>
--
Dmitry
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pwm: cros_ec: add __packed to prevent padding
2016-07-26 18:22 [PATCH] pwm: cros_ec: add __packed to prevent padding Brian Norris
2016-07-26 19:03 ` Dmitry Torokhov
@ 2016-07-26 20:15 ` Guenter Roeck
2016-09-05 6:44 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Guenter Roeck @ 2016-07-26 20:15 UTC (permalink / raw)
To: Brian Norris
Cc: Thierry Reding, linux-kernel, Brian Norris, linux-pwm,
Javier Martinez Canillas, Enric Balletbo, Dmitry Torokhov,
Gwendal Grignou
On Tue, Jul 26, 2016 at 11:22:13AM -0700, Brian Norris wrote:
> 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@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> ---
> 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;
> --
> 2.8.0.rc3.226.g39d4020
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pwm: cros_ec: add __packed to prevent padding
2016-07-26 18:22 [PATCH] pwm: cros_ec: add __packed to prevent padding Brian Norris
2016-07-26 19:03 ` Dmitry Torokhov
2016-07-26 20:15 ` Guenter Roeck
@ 2016-09-05 6:44 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Thierry Reding @ 2016-09-05 6:44 UTC (permalink / raw)
To: Brian Norris
Cc: linux-kernel, Brian Norris, linux-pwm, Javier Martinez Canillas,
Enric Balletbo, Dmitry Torokhov, Gwendal Grignou, Guenter Roeck
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On Tue, Jul 26, 2016 at 11:22:13AM -0700, Brian Norris wrote:
> 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@chromium.org>
> ---
> 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(-)
Applied, thanks.
Thierry
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^ permalink raw reply [flat|nested] 4+ messages in thread