Re: [PATCH RFC] x86: Fix 64-bit DMA masks on VIA

[Ingo Molnar <mingo@elte.hu>]

* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> > > > This untested patch is supposed to fix DMAing on some VIA 
> > > > boards. Currently the DMA subsystem returns an error, if the 
> > > > driver does tell that it supports a 64bit DMA mask. So the 
> > > > driver probing would fail in that case.
> > > 
> > > The driver is broken then. It is supposed to retry with a small 
> > > mask on an error. Please fix the driver.
> > 
> > I already added a workaround to the driver. Why do we need to 
> > workaround this in _every_ driver? (Note that _every_ driver 
> > supporting a 64bit mask is affected). Why not fix it in the DMA 
> > layer?
> 
> Some hardware wants to know it can get a given DMA mask or failure. I 
> agree however that a "pci_prefer_64bit_dma(pdev)" function would be a 
> good patch for someone to submit tot he PCI layer code.

yes, and i suspect Michael is correct in suggesting that the majority of 
drivers would use that interface and would let the PCI layer handle the 
probing/fallback details. (Jesse Cc:-ed)

	Ingo