netdev - Re: [PATCH net-next 16/19] net/mlx5: Implement dma ops and params for mediated device

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Message-ID: <20191108063731.GA24679@infradead.org>
Date:   Thu, 7 Nov 2019 22:37:31 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Parav Pandit <parav@...lanox.com>
Cc:     alex.williamson@...hat.com, davem@...emloft.net,
        kvm@...r.kernel.org, netdev@...r.kernel.org, saeedm@...lanox.com,
        kwankhede@...dia.com, leon@...nel.org, cohuck@...hat.com,
        jiri@...lanox.com, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next 16/19] net/mlx5: Implement dma ops and params
 for mediated device

On Thu, Nov 07, 2019 at 10:08:31AM -0600, Parav Pandit wrote:
> Implement dma ops wrapper to divert dma ops to its parent PCI device
> because Intel IOMMU (and may be other IOMMU) is limited to PCI devices.

Yikes.  I've been trying hard to get rid of pointless dma_map_ops
instance.  What upper layers use these child devices, and why can't
they just use the parent device for dma mapping directly?