On Wed, 2007-08-15 at 22:22 -0700, Randy Dunlap wrote:
> On Thu, 19 Jul 2007 10:49:30 -0700 Randy Dunlap wrote:
>
> > On Thu, 19 Jul 2007 18:57:50 +0300 Boaz Harrosh wrote:
> >
> > > Randy Dunlap wrote:
> > > >
> > > > Yes, this problem has been around forever AFAIK. You didn't add
> > > > to it.
> > > Do we need to file a bug report in Bugzilla or something, so people have
> > > a
> > > documentation of the work-around, until it is fixed?
> >
> > Wouldn't hurt, I guess, but the SCSI people know about it.
> >
> > > I think that for now I will wrap it up as it is. Could you send me the
> > > right
> > > BUG_ON() in place, with a printk pointing users to a solution? and I'll
> > > redo all the patches.
> >
> > I didn't add a BUG_ON(), so I don't have that patch.
> > (I just used a .slave_alloc function to force no high memory data
> > addresses, just like ppa.c does.)
> >
> > You could just do a BUG_ON() just before there is an outsw()
> > or insw() to a NULL pointer, e.g., in datao_run:
> >
> > BUG_ON(CURRENT_SC->SCp.ptr);
> >
> > or we could make building the driver depend on !HIGHMEM.
> >
> > I prefer either of the !HIGHMEM or slave_alloc changes to adding
> > a BUG_ON(). However, the SCSI people likely won't want to use the
> > slave_alloc() change because then the driver may never get fixed.
> > (Of course, it hasn't got fixed with the BUG happening either.)
> >
> > Anyway, I'll re-read Documentation/DMA*.txt to see if I can fix it.
>
>
> I have asked this once before, but I don't like the answer.
>
> Currently aha152x.c only works with !HIGHMEM due to highmem-pages
> not being mapped into the driver's memory space. James and hch
> tell me that using DMA mapping functions is the way to fix this,
> but those appear to me to be for DMA (!!), and this driver is (only)
> using PIO.
>
> I did try to use dma_map_sg() & dma_unmap_sg() here, but they end up
> giving the driver physical buffer addresses, which aren't what is
> needed for PIO. Should this driver be using
> scsi_kmap_atomic_sg() and scsi_kunmap_atomic_sg()
> or other API functions, or should the driver just use
> kmap_atomic() + kunmap_atomic()
> for each highmem page?
For DMA transfers ... which is where you give the device a bus physical
address and a length and tell it to go off and perform the transfer on
its own, you need to use the dma_map_ functions.
For PIO transfers, which are usually ones where you have to feed the
data into a special device register, since the kernel needs access to do
this, it has to be done via kmap_atomic()/kunmap_atomic(). So, if
everything has to go via pio, you use a sequence like
scsi_for_each_sg(cmd, sg, max, i) {
offset = sg->offset;
len = sg->len;
do {
coffset = offset; clen =len;
buf = scsi_kmap_atomic_sg(sg, 1, &coffset, &clen)
offset -= coffset; clen -= len;
<feed buf+coffset to/from PIO for clen>
scsi_kunmap_atomic_sg(buf);
} while (len > 0);
}
James
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