From mboxrd@z Thu Jan  1 00:00:00 1970
From: me@tobin.cc (Tobin C. Harding)
Date: Thu, 30 Mar 2017 11:39:16 +1100
Subject: 0 bit shift
In-Reply-To: <59220.1490831870@turing-police.cc.vt.edu>
References: <20170329225944.GG25014@eros>
	<59220.1490831870@turing-police.cc.vt.edu>
Message-ID: <20170330003916.GJ25014@eros>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Wed, Mar 29, 2017 at 07:57:50PM -0400, valdis.kletnieks at vt.edu wrote:
> On Thu, 30 Mar 2017 09:59:44 +1100, "Tobin C. Harding" said:
> > What is the reason for the zero bit shift in this code please?
> >
> > #define SDIO_STATE_PRESENT	(1<<0)		/* present in sysfs */
> >
> > file: include/linux/mmc/sdio_func.h
> 
> Most likely, to indicate that it's a bitmask in the 'unsigned int state'
> in the line above, rather than an integer.
> 
> See the other 2 uses of the flag in-tree:
> 
> [/usr/src/linux-next] git grep SDIO_STATE_PRESENT
> include/linux/mmc/sdio_func.h:#define SDIO_STATE_PRESENT        (1<<0)          /* present in sysfs */
> include/linux/mmc/sdio_func.h:#define sdio_func_present(f)      ((f)->state & SDIO_STATE_PRESENT)
> include/linux/mmc/sdio_func.h:#define sdio_func_set_present(f) ((f)->state |= SDIO_STATE_PRESENT)
> 

Awesome, thanks.