Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 16 Apr 2018 05:33:30 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     David Wang <davidwang@zhaoxin.com>
Cc:     tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        gregkh@linuxfoundation.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, brucechang@via-alliance.com,
        cooperyan@zhaoxin.com, qiyuanwang@zhaoxin.com,
        benjaminpan@viatech.com, lukelin@viacpu.com, timguo@zhaoxin.com
Subject: Re: [PATCH] x86/dma-mapping: override via_no_dac for new VIA PCI
 bridges
Message-ID: <20180416123330.GA6848@infradead.org>
References: <1523870816-6214-1-git-send-email-davidwang@zhaoxin.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1523870816-6214-1-git-send-email-davidwang@zhaoxin.com>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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?