Re: [RFC] Relaxed PIO read vs. DMA write ordering

[Jeremy Higdon <jeremy@sgi.com>]

On Wed, Jan 07, 2004 at 03:27:54PM -0800, Greg KH wrote:
> On Wed, Jan 07, 2004 at 03:07:12PM -0800, Jesse Barnes wrote:
> > 
> >   1) add pcix_enable_relaxed() and read_relaxed() (read() would always be
> >      ordered)
> 
> This probably preserves the current situation best, enabling driver
> writers to be explicit in knowing what is happening.
> 
> thanks,
> 
> greg k-h

I like this best too.  That way, a driver can enable a relaxed read
in the performance path and not have to audit the other reads.

So in a generic PCI driver, you'd call pcix_enable_relaxed() and
then use read() for initialization, error recovery, etc., and
use read_relaxed() in the main execution path where it is determined
to be safe.

The default would be the standard behavior that we have.

One question I have is what the need for pcix_enable_relaxed() is.
Are we thinking that this sets some bit in one or more registers?
What happens if you use read_relaxed() and you didn't call
pcix_enable_relaxed() previously?

jeremy