Re: [PATCH 1/6] canfd: add new data structures and constants

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 06/18/2012 09:19 PM, Oliver Hartkopp wrote:
> On 18.06.2012 21:13, Marc Kleine-Budde wrote:
> 
>> On 06/18/2012 07:39 PM, Oliver Hartkopp wrote:
>>> - add new struct canfd_frame
> 
>>>  struct can_frame {
>>>  	canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
>>> -	__u8    can_dlc; /* data length code: 0 .. 8 */
>>> +	__u8    can_dlc; /* frame payload length in byte (0 .. 8) */
>>>  	__u8    data[8] __attribute__((aligned(8)));
>>
>> checkpatch complains:
>>
>> WARNING: __aligned(size) is preferred over __attribute__((aligned(size)))
>> #84: FILE: include/linux/can.h:102:
>> +       __u8    data[64] __attribute__((aligned(8)));
>>
>> total: 0 errors, 1 warnings, 97 lines checked

> Hm, yes. I wanted to have it the same way as in struct can_frame.

> I wonder if "__aligened(size)" is also compatible for backports - or
> alternative if we should also modify the original can_frame:

__aligened(size) has been introduced in v2.6.21-rc1~91^2~274.

(How to figure out:
$ git blame include/linux/compiler-gcc.h
$ git describe 82ddcb04
v2.6.20-1507-g82ddcb0
$ git describe --contains 82ddcb04
v2.6.21-rc1~91^2~274
)

>>> - 	__u8    data[8] __attribute__((aligned(8)));
>>> + 	__u8    data[8] __aligned(8);

If you want to be super clean you can first make a patch that changes
the existing __attribute__((aligned(8))) to __aligned(8), and then add
your canfd series. If not, just mention it in the patch description
(While being here change can_fd to __aligned(8)).

Err..this is a userspace header, I just tested it, headers_install
doesn't remove it. And userspace fails to compile with this. For now
stick to __attribute__((aligned(8))).

Marc

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