Re: [PATCH] x86/dma-mapping: override via_no_dac for new VIA PCI bridges

From: Thomas Gleixner
Date: Tue Apr 17 2018 - 09:33:32 EST

On Tue, 17 Apr 2018, 'Christoph Hellwig' wrote:
> On Tue, Apr 17, 2018 at 10:54:37AM +0200, Thomas Gleixner wrote:
> > The question was rather to have a list of PCI IDs for those chipsets which
> > have the problem and set the 'disable' flag only for those. That makes a lot
> > more sense than making a list of new chips which disable the disable flag.
> Agreed.
> There are a few other things I'd like to do in this area while we're
> at it (I'm happy to do the work, not trying to offload it to David
> or Thomas):
> (1) make the nodac flag a per-device flag. Set for every device
> under one of the affected VIA bridges, or for all PCI devices
> if the nodac command line option is used
> (2) move that flag into the common struct device (or the to be
> designed dma struct hanging off it in the future) and make that
> bit handled in common code as there is a common Xilinx host
> bridge with a 32-bit dma limitation
> (3) kill of the forcesac option, which was a strange performance
> tweak back in plain PCI days, which probably didn't even work
> as expected to start with.

Sounds good.