Use of data types

Use of data types

[Khushhua Mogambo]

Hi
  I starting to port Linux kernel to my companies new ARM based
SoC and development board.

Some of the regs is 16bits wide and some is 32bits width. I ask if
my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
in the whole porting would be acceptable or not?

In different wording, using only u16 and u32 always is considered good
quality or bad?

many thanks.

Use of data types

[Uwe Kleine-König]

Hello,

On Mon, Jan 18, 2010 at 09:43:12PM +0900, Khushhua Mogambo wrote:
> Hi
>   I starting to port Linux kernel to my companies new ARM based
> SoC and development board.
> 
> Some of the regs is 16bits wide and some is 32bits width. I ask if
> my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
> in the whole porting would be acceptable or not?
> 
> In different wording, using only u16 and u32 always is considered good
> quality or bad?
I prefer using u32 over int.  Still more if your register space isn't uniform.

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-K?nig            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |

Use of data types

[Matthias Kaehlcke]

El Mon, Jan 18, 2010 at 02:41:20PM +0100 Uwe Kleine-K?nig ha dit:

> On Mon, Jan 18, 2010 at 09:43:12PM +0900, Khushhua Mogambo wrote:
> > Hi
> >   I starting to port Linux kernel to my companies new ARM based
> > SoC and development board.
> > 
> > Some of the regs is 16bits wide and some is 32bits width. I ask if
> > my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
> > in the whole porting would be acceptable or not?
> > 
> > In different wording, using only u16 and u32 always is considered good
> > quality or bad?
> I prefer using u32 over int.  Still more if your register space isn't uniform.

ditto

how about using the C99 types uint32_t, ... in the kernel? 

-- 
Matthias Kaehlcke
Embedded Linux Developer
Barcelona

              Insanity: doing the same thing over and over
                again and expecting different results
                            (Albert Einstein)
                                                                 .''`.
    using free software / Debian GNU/Linux | http://debian.org  : :'  :
                                                                `. `'`
gpg --keyserver pgp.mit.edu --recv-keys 47D8E5D4                  `-

Use of data types

[Russell King - ARM Linux]

On Mon, Jan 18, 2010 at 02:42:15PM +0100, Matthias Kaehlcke wrote:
> El Mon, Jan 18, 2010 at 02:41:20PM +0100 Uwe Kleine-K?nig ha dit:
> 
> > On Mon, Jan 18, 2010 at 09:43:12PM +0900, Khushhua Mogambo wrote:
> > > Hi
> > >   I starting to port Linux kernel to my companies new ARM based
> > > SoC and development board.
> > > 
> > > Some of the regs is 16bits wide and some is 32bits width. I ask if
> > > my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
> > > in the whole porting would be acceptable or not?
> > > 
> > > In different wording, using only u16 and u32 always is considered good
> > > quality or bad?
> > I prefer using u32 over int.  Still more if your register space isn't uniform.
> 
> ditto
> 
> how about using the C99 types uint32_t, ... in the kernel? 

You might want to read Documentation/CodingStyle chapter 5, which covers
some of these issues.

Use of data types

[Khushhua Mogambo]

On Mon, Jan 18, 2010 at 10:58 PM, Sergei Shtylyov
<sshtylyov@ru.mvista.com> wrote:
> Hello.
>
> Matthias Kaehlcke wrote:
>
>>>> Hi
>>>> ?I starting to port Linux kernel to my companies new ARM based
>>>> SoC and development board.
>>>>
>>>> Some of the regs is 16bits wide and some is 32bits width. I ask if
>>>> my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
>>>> in the whole porting would be acceptable or not?
>>>>
>>>> In different wording, using only u16 and u32 always is considered good
>>>> quality or bad?
>>>>
>>>
>>> I prefer using u32 over int. ?Still more if your register space isn't
>>> uniform.
>>>
>>
>> ditto
>>
>> how about using the C99 types uint32_t, ... in the kernel?
>
> ?They are actually used in some places but this is generally frowned upon.
> They are for userspace.
>
> WBR, Sergei

from thread, i understand that u32 is encouraged whenever we have reason. I m
going to use u8,16,32 heavily.

Thanks to every one who replied and helped me.

Use of data types

[Russell King - ARM Linux]

On Tue, Jan 19, 2010 at 08:57:03PM +0900, Khushhua Mogambo wrote:
> from thread, i understand that u32 is encouraged whenever we have reason. I m
> going to use u8,16,32 heavily.

Incorrect.

As I said, use u8,u16,u32 when you need something that's of that size
(eg, for storing values from hardware registers.)  If you don't require
something of a specific size, then don't use them.

Use of data types

[Khushhua Mogambo]

On Wed, Jan 20, 2010 at 2:42 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Tue, Jan 19, 2010 at 08:57:03PM +0900, Khushhua Mogambo wrote:
>> from thread, i understand that u32 is encouraged whenever we have reason. I m
>> going to use u8,16,32 heavily.
>
> Incorrect.
>
> As I said, use u8,u16,u32 when you need something that's of that size
> (eg, for storing values from hardware registers.) ?If you don't require
> something of a specific size, then don't use them.
ok I undrstand. thanking you very much.

Use of data types

[Ben Dooks]

On Tue, Jan 19, 2010 at 08:57:03PM +0900, Khushhua Mogambo wrote:
> On Mon, Jan 18, 2010 at 10:58 PM, Sergei Shtylyov
> <sshtylyov@ru.mvista.com> wrote:
> > Hello.
> >
> > Matthias Kaehlcke wrote:
> >
> >>>> Hi
> >>>> ?I starting to port Linux kernel to my companies new ARM based
> >>>> SoC and development board.
> >>>>
> >>>> Some of the regs is 16bits wide and some is 32bits width. I ask if
> >>>> my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
> >>>> in the whole porting would be acceptable or not?
> >>>>
> >>>> In different wording, using only u16 and u32 always is considered good
> >>>> quality or bad?
> >>>>
> >>>
> >>> I prefer using u32 over int. ?Still more if your register space isn't
> >>> uniform.
> >>>
> >>
> >> ditto
> >>
> >> how about using the C99 types uint32_t, ... in the kernel?
> >
> > ?They are actually used in some places but this is generally frowned upon.
> > They are for userspace.
> >
> > WBR, Sergei
> 
> from thread, i understand that u32 is encouraged whenever we have reason. I m
> going to use u8,16,32 heavily.

It can depend on where it is being used, passing u8 and u16 around from
function to function can cost as the compiler tends to output code
to restrict the range of the registers' contents, thus u32 can end up
being a better choice.

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.

Use of data types

[Russell King - ARM Linux]

On Mon, Jan 18, 2010 at 02:41:20PM +0100, Uwe Kleine-K?nig wrote:
> Hello,
> 
> On Mon, Jan 18, 2010 at 09:43:12PM +0900, Khushhua Mogambo wrote:
> > Hi
> >   I starting to port Linux kernel to my companies new ARM based
> > SoC and development board.
> > 
> > Some of the regs is 16bits wide and some is 32bits width. I ask if
> > my using u16 and u32 in place of 'unsigned short' and 'unsigned int'
> > in the whole porting would be acceptable or not?
> > 
> > In different wording, using only u16 and u32 always is considered good
> > quality or bad?
> I prefer using u32 over int.  Still more if your register space isn't uniform.

u32 should be used for things that you want to be an unsigned 32-bit and
nothing else.  int and unsigned int for integers where the size doesn't
matter that much.

So, if you want a data type that is unsigned 32-bit, use u32.  If not,
use unsigned int or similar.