linux-kernel - Re: [PATCH] x86/dma-mapping: override via_no

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Date:   Tue, 17 Apr 2018 10:54:37 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Wang <davidwang@...oxin.com>
cc:     'Christoph Hellwig' <hch@...radead.org>, mingo@...hat.com,
        hpa@...or.com, gregkh@...uxfoundation.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, brucechang@...-alliance.com,
        cooperyan@...oxin.com, qiyuanwang@...oxin.com,
        benjaminpan@...tech.com, lukelin@...cpu.com, timguo@...oxin.com
Subject: Re: [PATCH] x86/dma-mapping: override via_no_dac for new VIA PCI
 bridges

On Tue, 17 Apr 2018, David Wang wrote:
> > On Mon, Apr 16, 2018 at 05:26:56PM +0800, David Wang wrote:
> > > PCI bridges integrated in new VIA chipset/SoC have no DAC issue.
> > > Enable DAC for the platforms with these chipset/SoC can improve DMA
> > > performance about 20% when DRAM size > 4GB.
> > >
> > 
> > So we get an exception to an exception?  Is there any way to figure out
> the
> > PCI IDs actually affected?
> Yes.
> 
> Do you mean we should list the PCI IDs of the PCI bridges which have no DAC
> issue?

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.

Thanks,

	tglx