From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932296AbcGZSWp (ORCPT ); Tue, 26 Jul 2016 14:22:45 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:33363 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757803AbcGZSWk (ORCPT ); Tue, 26 Jul 2016 14:22:40 -0400 From: Brian Norris To: Thierry Reding Cc: , Brian Norris , linux-pwm@vger.kernel.org, Javier Martinez Canillas , Enric Balletbo , Dmitry Torokhov , Gwendal Grignou , Guenter Roeck , Brian Norris Subject: [PATCH] pwm: cros_ec: add __packed to prevent padding Date: Tue, 26 Jul 2016 11:22:13 -0700 Message-Id: <1469557333-9497-1-git-send-email-briannorris@chromium.org> X-Mailer: git-send-email 2.8.0.rc3.226.g39d4020 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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