linux-kernel - Re: [RFC PATCH V2 net-next 03/11] net: hibmcge: Add mdio and hardware configuration supported in this module

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Message-ID: <1ff7ba7c-3a25-46b5-a9de-a49d96926e64@huawei.com>
Date: Fri, 16 Aug 2024 14:10:36 +0800
From: Jijie Shao <shaojijie@...wei.com>
To: Andrew Lunn <andrew@...n.ch>
CC: <shaojijie@...wei.com>, <yisen.zhuang@...wei.com>,
	<salil.mehta@...wei.com>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
	<shenjian15@...wei.com>, <wangpeiyang1@...wei.com>, <liuyonglong@...wei.com>,
	<sudongming1@...wei.com>, <xujunsheng@...wei.com>, <shiyongbang@...wei.com>,
	<jdamato@...tly.com>, <jonathan.cameron@...wei.com>,
	<shameerali.kolothum.thodi@...wei.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH V2 net-next 03/11] net: hibmcge: Add mdio and hardware
 configuration supported in this module


on 2024/8/16 10:25, Andrew Lunn wrote:
>> +struct hbg_mdio_command {
>> +	union {
>> +		struct {
>> +			u32 mdio_devad : 5;
>> +			u32 mdio_prtad :5;
>> +			u32 mdio_op : 2;
>> +			u32 mdio_st : 2;
>> +			u32 mdio_start : 1;
>> +			u32 mdio_clk_sel : 1;
>> +			u32 mdio_auto_scan : 1;
>> +			u32 mdio_clk_sel_exp : 1;
>> +			u32 rev : 14;
>> +		};
>> +		u32 bits;
>> +	};
>> +};
> This is generally not the way to do this. Please look at the macros in
> include/linux/bitfield.h. FIELD_PREP, GENMASK, BIT, FIELD_GET
> etc. These are guaranteed to work for both big and little endian, and
> you avoid issues where the compiler decides to add padding in your
> bitfields.
>
> 	Andrew

Thanks, I already know about macros like FIELD_PREP or FIELD_GET.
and these macros are already used in parts of this patch set.

But I think this writing style in here very convenient.
Although padding needs to be added during definition,
but you can use command.mdio_start or command->mdio_start
to access specific bitfields.

Although FIELD_PREP/FIELD_GET is convenient,
But it also needs to define the mask using BIT or GENMASK,
and the mask can only be a static constant,
which makes it difficult to use sometimes.

Thanks a lot!
	
	Jijie Shao