netdev - Re: [PATCH net-next 8/8] net: phy: use '__packed' instead of '__attribute__((__packed_

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Date:   Wed, 16 Jun 2021 06:17:18 +0000
From:   liweihang <liweihang@...wei.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        liangwenpeng <liangwenpeng@...wei.com>,
        "quentin.schulz@...tlin.com" <quentin.schulz@...tlin.com>,
        "antoine.tenart@...tlin.com" <antoine.tenart@...tlin.com>
Subject: Re: [PATCH net-next 8/8] net: phy: use '__packed' instead of
 '__attribute__((__packed__))'

On 2021/6/14 22:28, David Laight wrote:
> From: Weihang Li
>> Sent: 11 June 2021 07:37
>>
>> Prefer __packed over __attribute__((__packed__)).
>>
>> Signed-off-by: Wenpeng Liang <liangwenpeng@...wei.com>
>> Signed-off-by: Weihang Li <liweihang@...wei.com>
>> ---
>>  drivers/net/phy/mscc/mscc_ptp.h | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/phy/mscc/mscc_ptp.h b/drivers/net/phy/mscc/mscc_ptp.h
>> index da34653..01f78b4 100644
> ...
>>  /* Represents an entry in the timestamping FIFO */
>>  struct vsc85xx_ts_fifo {
>>  	u32 ns;
>>  	u64 secs:48;
>>  	u8 sig[16];
>> -} __attribute__((__packed__));
>> +} __packed;
> 
> Hmmmm I'd take some convincing that 'u64 secs:48' is anything
> other than 'implementation defined'.
> So using it to map a hardware structure seems wrong.
> 
> If this does map a hardware structure it ought to have
> 'endianness' annotations.
> If it doesn't then why the bitfield and why packed?
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
> 

Hi David,

Thank you for your attention. You are right, I found the contents of structure
vsc85xx_ts_fifo is got from hardware. But I'm not sure if any issues or warnings
will be introduced into this driver after just changing 'u64 secs:48' to '__be64
secs:48'.

Let's keep this patch as it is. I cc the developers of the code, maybe they
didn't realize it or had some reasons to define it like that.

Thanks
Weihang