Re: [Linux-ia64] _raw_write_trylock() missing

From: Joel GUILLET <Joel.Guillet_at_bull.net>
Date: 2003-02-05 19:39:48
Hello,

On Wed, 5 Feb 2003, Ian Wienand wrote:

> On Tue, Feb 04, 2003 at 03:18:22PM +0100, Joel GUILLET wrote:
> > What the macro is doing : (at least, what I think it is doing)
> >
> > - if the actual lock value is equal to "0",
> > 	change the lock value to "00.....0001"

Sorry for that mistake in my mail, but the value I actually want to store
into the lock is the 32 bit value "1000000...000".

... because the rw_lock value is composed with :
- 1 bit for the write "flag" (the most significant bit of a _long_ value)
- 31 bits for the read flags

... so the value of r29 (0x80000000) should be OK.


> > 	else do nothing
> >
> > The code for this : (in include/asm-ia64/spinlock.h)
> > 		"dep r29 = -1, r0, 31, 1\n"
>
> doesn't this make the value of r29 0x80000000?  i.e the 1 is at the
> wrong end.
>
> > 		"cmpxchg4.acq result = [rw], r29, ar.ccv\n"
>
> so here you end up swapping 0x8000000 into rw if rw=0
>
> i think maybe just making doing mov r29 = 1 above will do what you
> want.
>
> -i
> ianw@gelato.unsw.edu.au
> http://www.gelato.unsw.edu.au
>
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Received on Wed Feb 05 00:39:30 2003

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