linux-kernel - Re: [RFC][PATCH] apparent big-endian bugs in dwc-xlgmac

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Date:   Mon, 11 Dec 2017 14:46:47 +0800
From:   Jie Deng <Jie.Deng1@...opsys.com>
To:     Al Viro <viro@...IV.linux.org.uk>,
        Jie Deng <Jie.Deng1@...opsys.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH] apparent big-endian bugs in dwc-xlgmac

On 2017/12/11 13:38, Al Viro wrote:

> On Mon, Dec 11, 2017 at 05:05:20AM +0000, Al Viro wrote:
>
>> What for?  Sure, this variant will work, but why bother with
>> 	a = le32_to_cpu(b);
>> 	(cpu_to_le32(a) & ....) | ....
>> and how is that better than
>> 	(b & ...) | ...
>>
>> IDGI...  Mind you, I'm not sure if there is any point keeping _var in that thing,
>> seeing that we use var only once - might be better off with
>> 	((var) & ~cpu_to_le32(GENMASK(_pos + _len - 1, _pos))) | 	\
>> 		cpu_to_le32(_val);					\
> FWIW, seeing how many drivers end up open-coding that, I'm rather tempted to
> add to linux/bitops.h or linux/byteorder/generic.h the following:
>
> static inline __le16 le16_replace_bits(__le16 old, u16 v, int bit, int size)
> {
> 	__le16 mask = cpu_to_le16(GENMASK(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_le16(v << bit) & mask);
> }
>
> static inline __le32 le32_replace_bits(__le32 old, u32 v, int bit, int size)
> {
> 	__le32 mask = cpu_to_le32(GENMASK(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_le32(v << bit) & mask);
> }
>
> static inline __le64 le64_replace_bits(__le64 old, u64 v, int bit, int size)
> {
> 	__le64 mask = cpu_to_le64(GENMASK_ULL(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_le64(v << bit) & mask);
> }
>
> static inline __be16 be16_replace_bits(__be16 old, u16 v, int bit, int size)
> {
> 	__be16 mask = cpu_to_be16(GENMASK(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_be16(v << bit) & mask);
> }
>
> static inline __be32 be32_replace_bits(__be32 old, u32 v, int bit, int size)
> {
> 	__be32 mask = cpu_to_be32(GENMASK(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_be32(v << bit) & mask);
> }
>
> static inline __be64 be64_replace_bits(__be64 old, u64 v, int bit, int size)
> {
> 	__be64 mask = cpu_to_be64(GENMASK_ULL(bit + size - 1, bit));
> 	return (old & ~mask) | (cpu_to_be64(v << bit) & mask);
> }
>
> static inline u16 le16_get_bits(__le16 v, int bit, int size)
> {
> 	return (le16_to_cpu(v) >> bit) & (BIT(size) - 1);
> }
>
> static inline u32 le32_get_bits(__le32 v, int bit, int size)
> {
> 	return (le32_to_cpu(v) >> bit) & (BIT(size) - 1);
> }
>
> static inline u64 le64_get_bits(__le64 v, int bit, int size)
> {
> 	return (le64_to_cpu(v) >> bit) & (BIT_ULL(size) - 1);
> }
>
> static inline u16 be16_get_bits(__be16 v, int bit, int size)
> {
> 	return (be16_to_cpu(v) >> bit) & (BIT(size) - 1);
> }
>
> static inline u32 be32_get_bits(__be32 v, int bit, int size)
> {
> 	return (be32_to_cpu(v) >> bit) & (BIT(size) - 1);
> }
>
> static inline u64 be64_get_bits(__be64 v, int bit, int size)
> {
> 	return (be64_to_cpu(v) >> bit) & (BIT_ULL(size) - 1);
> }
>
> and let drivers use those...
Sounds good. As a driver developer, I'm happy to see this.