linux-kernel - Re: [PATCH 4/5] misc: vop: set VIRTIO_F_ACCESS

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Message-ID: <20200928060917.GB9387@infradead.org>
Date:   Mon, 28 Sep 2020 07:09:17 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Sherry Sun <sherry.sun@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "sudeep.dutt@...el.com" <sudeep.dutt@...el.com>,
        "ashutosh.dixit@...el.com" <ashutosh.dixit@...el.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "wang.yi59@....com.cn" <wang.yi59@....com.cn>,
        "rikard.falkeborn@...il.com" <rikard.falkeborn@...il.com>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "mst@...hat.com" <mst@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 4/5] misc: vop: set VIRTIO_F_ACCESS_PLATFORM for
 nocoherent platform

On Sun, Sep 27, 2020 at 08:05:07AM +0000, Sherry Sun wrote:
> Hi Christoph,
> 
> > On Fri, Sep 25, 2020 at 03:26:29PM +0800, Sherry Sun wrote:
> > > Set VIRTIO_F_ACCESS_PLATFORM feature for nocoherent platform, since it
> > > needs the DMA API for virtio.
> > 
> > Given that VOP is a plug-in PCIe card VIRTIO_F_ACCESS_PLATFORM must
> > always be set, as the DMA mapping details are not something the virtio
> > implementation decides on, but the host PCIe/iommu implementation.
> 
> So do you mean that we should remove the check, and set VIRTIO_F_ACCESS_PLATFORM feature directly?

Yes.  In a separate prep patch.