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Date: Tue, 31 Mar 2026 11:39:36 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Zhiping Zhang <zhipingz@meta.com>
Cc: Keith Busch <kbusch@kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
	Bjorn Helgaas <bhelgaas@google.com>, linux-rdma@vger.kernel.org,
	linux-pci@vger.kernel.org, netdev@vger.kernel.org,
	dri-devel@lists.freedesktop.org, Yochai Cohen <yochai@nvidia.com>,
	Yishai Hadas <yishaih@nvidia.com>,
	Bjorn Helgaas <helgaas@kernel.org>
Subject: Re: [RFC v2 1/2] vfio: add callback to get tph info for dmabuf
Message-ID: <20260331083936.GB814676@unreal>
References: <20260324234615.3731237-1-zhipingz@meta.com>
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 <20260325082534.GN814676@unreal>
 <acW2BwQKaUbS3eL9@kbusch-mbp>
 <CAH3zFs1nbAKpYxwzMcwpC_Sdy+3tE0n0wUzxJ411gV-q1O++qQ@mail.gmail.com>
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On Thu, Mar 26, 2026 at 03:55:44PM -0700, Zhiping Zhang wrote:
> On Thu, Mar 26, 2026 at 3:41 PM Keith Busch <kbusch@kernel.org> wrote:
> >
> > >
> > On Wed, Mar 25, 2026 at 10:25:34AM +0200, Leon Romanovsky wrote:
> > > On Tue, Mar 24, 2026 at 04:46:02PM -0700, Zhiping Zhang wrote:
> > > >  struct vfio_device_feature_dma_buf {
> > > >     __u32   region_index;
> > > >     __u32   open_flags;
> > > > -   __u32   flags;
> > > > -   __u32   nr_ranges;
> > > > +   __u32   flags;
> > > > +#define VFIO_DMABUF_FL_TPH         (1U << 0) /* TPH info is present */
> > > > +#define VFIO_DMABUF_TPH_PH_SHIFT   1         /* bits 1-2: PH (2-bit) */
> > > > +#define VFIO_DMABUF_TPH_PH_MASK    0x6U
> > > > +#define VFIO_DMABUF_TPH_ST_SHIFT   16        /* bits 16-31: steering tag */
> > > > +#define VFIO_DMABUF_TPH_ST_MASK            0xffff0000U
> > >
> > > This extension of flags is basically kills future extension of this
> > > struct for anything that includes TPH.
> > >
> > > Add new
> > > enum vfio_device_feature_dma_buf_flags {
> > >     VFIO_DMABUF_FL_TPH  = 1 << 0
> > > }
> 
> yes we can do that.
> 
> > >
> > > > +   __u32   nr_ranges;
> > >
> > > add your "__u16 steering_tag" and "__u8 ph" fields here.
> >
> That is what I did in V1, Leon.

Not really, you did only half of the work. You didn't introduce new flag
and didn't calculate "old dma range" position.

Thanks