Re: unchecked_isa_dma and BusLogic SCSI controller

[Christoph Hellwig <hch@infradead.org>]

On Thu, Nov 02, 2006 at 05:41:28AM -0700, Matthew Wilcox wrote:
> On Wed, Nov 01, 2006 at 05:33:58PM -0800, Randy Dunlap wrote:
> >     unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
> >                    restriction), 0=>can use full 32 bit (or better) DMA
> >                    address space
> > 
> > > It is hard for me to see why BusLogic controller would only do DMA
> > > in low 16MB.  Is there a fix for this?
> > 
> > Does anyone know that controller hardware and its limitations?
> 
> I don't, but:
> 
> 		if (pci_set_dma_mask(PCI_Device, DMA_32BIT_MASK ))
> 			continue;
> 
> So somebody thinks the device can do 32-bit addressing.  I would expect
> that setting unchecked_isa_dma is a historical mistake.  However, I
> don't have any cards of this type to test.

The buslogic driver also supports non-PCI devices, and at least the
ISA boards have the obvious limitiation that unchecked_isa_dma = 1
caters to.  Now someone would have to audit the driver whether it's
enough to only set this on the actual isa hosts instead of the host
template.