linux-kernel - Re: [PATCH] bitops: Introduce BITS_PER

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Message-ID: <153090001992.7594.17876223022816534941@cwilso3-mobl.ger.corp.intel.com>
Date:   Fri, 06 Jul 2018 19:00:20 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Andy Gospodarek <gospo@...adcom.com>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] bitops: Introduce BITS_PER_TYPE

Quoting Randy Dunlap (2018-07-06 18:55:57)
> On 07/06/18 10:51, Chris Wilson wrote:
> > Quoting Randy Dunlap (2018-07-06 18:48:55)
> >>
> >> On 07/06/18 02:44, Chris Wilson wrote:
> >>> net_dim.h has a rather useful extension to BITS_PER_BYTE to compute the
> >>> number of bits in a type (BITS_PER_BYTE * sizeof(T)), so promote the
> >>> macro to bitops.h, alongside BITS_PER_BYTE, for wider usage.
> >>>
> >>> Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> >>> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> >>> Cc: Andy Gospodarek <gospo@...adcom.com>
> >>> Cc: David S. Miller <davem@...emloft.net>
> >>> Cc: Thomas Gleixner <tglx@...utronix.de>
> >>> Cc: Andrew Morton <akpm@...ux-foundation.org>
> >>> Cc: Ingo Molnar <mingo@...nel.org>
> >>> ---
> >>>  include/linux/bitops.h  | 3 ++-
> >>>  include/linux/net_dim.h | 1 -
> >>>  2 files changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> >>> index 4cac4e1a72ff..091cb17d1a9b 100644
> >>> --- a/include/linux/bitops.h
> >>> +++ b/include/linux/bitops.h
> >>> @@ -11,7 +11,8 @@
> >>>  #define BIT_ULL_MASK(nr)     (1ULL << ((nr) % BITS_PER_LONG_LONG))
> >>>  #define BIT_ULL_WORD(nr)     ((nr) / BITS_PER_LONG_LONG)
> >>>  #define BITS_PER_BYTE                8
> >>> -#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
> >>> +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
> >>> +#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
> >>>  #endif
> >>>  
> >>>  /*
> >>
> >> doesn't <linux/net_dim.h> need to #include <linux/bitops.h> ?
> > 
> > It already has to in order to obtain BITS_PER_BYTE. Just doesn't do so
> > directly.
> 
> Right.  and does that work on all $ARCHes?

It's a pre-existing dependency in the header, net_dim.h cannot
compile unless BITS_PER_BYTE is defined i.e. bitops.h is included.
The patch does not affect that.
-Chris