> On Thu, Nov 12, 1998 at 03:59:38PM +0100, Kurt Garloff wrote:
> > Reading this, I wonder, why my kernel with PAGE_OFFSET 0x70000000 does work.
> > Somebody able to explain this?
>
> And it crashes with an ,,Unable to handle kernel paging request at
> e4414007`` in the ncr53c8xx (3.0i) driver, if I apply the following patch.
> So is the idea about what it should look like wrong, or is it the ncr53c8xx
> driver?
For DMAing from devices, drivers call virt_to_bus() that provides the
address devices have to use to hit the right memory location from the bus.
Being wrong is harder then being right for that, but obviously a bug is
always possible.
> --- linux/include/asm-i386/io.h~ Thu Nov 12 10:52:46 1998
> +++ linux/include/asm-i386/io.h Thu Nov 12 15:55:55 1998
> @@ -101,8 +101,8 @@
> #include <linux/vmalloc.h>
> #include <asm/page.h>
>
> -#define __io_virt(x) ((void *)(PAGE_OFFSET | (unsigned long)(x)))
> -#define __io_phys(x) ((unsigned long)(x) & ~PAGE_OFFSET)
> +#define __io_virt(x) ((void *)(PAGE_OFFSET + (unsigned long)(x)))
> +#define __io_phys(x) ((unsigned long)(x) - PAGE_OFFSET)
Only the __io_phys(x) macro should be involved in virt_to_bus().
The previous versions of the macros left result unchanged if they are
called more than once, but your versions will break. So probably
such a bug exists somewhere.
BTW, what was wrong with previous macro versions?
(Sorry, if I just missed your initial posting. Will search it).
Regards,
Gerard.
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