Subject: Re: MPC8349ea Random Device Generator driver

From: [email-masked] (Olof Johansson)
Date: Thu, 7 Jun 2007 10:20:41 -0500

On Thu, Jun 07, 2007 at 09:23:35AM -0500, Timur Tabi wrote:
> Olof Johansson wrote:
> >On Wed, Jun 06, 2007 at 05:32:19PM -0500, Timur Tabi wrote:
> >>Olof Johansson wrote:
> >>
> >>> - you can never assign a __le16 type to any other integer type or any 
> >>>   other bitwise type. You'd get a warnign about incompatible types. 
> >>>   Makes sense, no?
> >>Then why do the in_be functions return an unsigned int instead of a __be 
> >>type?  Isn't that effectively removing the endian-ness from the type?
> >
> >Because they read a big endian register and returns the contents in the
> >native byte order for the machine.
> 
> In other words, the in_le16() function exists so that we can "assign a 
> __le16 type to any other integer type or any other bitwise type."

No. in_le16 exists so you can read a little-endian 16 bit register on
a device, and store it to a regular 16-bit integer variable. It
has nothing to do with assignment.

__le16 is just a type with hints for the programmer: "Hey, this is a
16-bit variable, but we're storing it in little-endian format. So if you
need to use it as a native data type, you need to swap it by hand first",
and sparse is able to help you find places where you didn't.

If you use the accessors to read/write hardware (as you are supposed to
do), then you don't need special types in your structs, just make sure
you use the right accessors.

-Olof