linux-kernel - Re: [PATCH v3 3/4] staging: rtl8723bs: use ether_addr_copy() in rtw_macaddr

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Message-ID: <6221958a-f817-e01b-7e0f-adbbba9acde4@gmail.com>
Date:   Wed, 27 Jun 2018 14:56:00 +0200
From:   Michael Straube <straube.linux@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Joe Perches <joe@...ches.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] staging: rtl8723bs: use ether_addr_copy() in
 rtw_macaddr_cfg()

Am 27.06.2018 um 10:33 schrieb Dan Carpenter:
> On Tue, Jun 26, 2018 at 10:32:09PM +0200, Michael Straube wrote:
>>
>> On 06/26/18 22:17, Joe Perches wrote:
>>> On Tue, 2018-06-26 at 21:44 +0200, Michael Straube wrote:
>>>> On 06/26/18 19:32, Andy Shevchenko wrote:
>>>>> On Tue, Jun 26, 2018 at 11:14 AM, Michael Straube
>>>>> <straube.linux@...il.com> wrote:
>>>>>> Use ether_addr_copy() instead of memcpy() to copy the mac address.
>>>>>>
>>>>>
>>>>> Suggested-by ?
>>>>>
>>>>
>>>> I'll add it. Sorry, I was not aware of the Suggested-by tag.
>>>>
>>>>> Btw, ensure that the source and destination buffers are aligned to u16
>>>>> as required by API.
>>>>
>>>> To be honest I'm not sure how to do that excactly.
>>>>
>>>> Use __align(2) in the array declarations? e.g.:
>>>>
>>>>            u8 mac[ETH_ALEN] __align(2);
>>>
>>> All initial function automatics are naturally aligned.
>>>>
>> So there is nothing to change? Now I'm confused.
> 
> Do not add the __align(2), as Joe says, it's not required.  You just
> need to C alignment rules (it's expected/required for this sort of
> patch).
> 
> Like if you have a struct:
> 
> struct foo {
> 	char a;
> 	int b;
> };
> 
> There is going to be a 3 byte gap between a and b because ints are
> normally __align(4).  The exception is when the struct is __packed.  So
> sizeof(struct foo) in this case is going to be 8.  kmalloc() returns
> pointers which are 8 at least byte aligned normally.  See
> ARCH_KMALLOC_MINALIGN.  There is one arch where it's 4 byte aligned?
> 
> So when you would get things which aren't __align(2) is when you have:
> 
> struct bar {
> 	char a[3];
> 	u8 mac[ETH_ALEN];
> };
> 
> Here the struct member before the mac[] is an odd number of char.  Or
> when the struct is packed.
> 
> regards,
> dan carpenter
> 

Thank you for your explanation. I will not add __aligned(2).
The other buffer is u32 aligned:

struct eeprom_priv
{
         u8 bautoload_fail_flag;
         u8 bloadfile_fail_flag;
         u8 bloadmac_fail_flag;
         u8 EepromOrEfuse;

         u8 mac_addr[6]; /* PermanentAddress */

	...

         u32     ocr;

	...
};

Should I add a thanks line to the commit message:

     Thanks to Dan Carpenter, Joe Perches and Andy Shevchenko.

Or would that be considered as too much?

Regards
Michael