linux-kernel - Re: [RFC net-next v1 1/3] vfio/mdev: Inherit dma masks of parent device

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Date:   Fri, 8 Mar 2019 15:32:43 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Parav Pandit <parav@...lanox.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        michal.lkml@...kovi.net, davem@...emloft.net,
        gregkh@...uxfoundation.org, jiri@...lanox.com,
        kwankhede@...dia.com, vuhuong@...lanox.com, yuvalav@...lanox.com,
        jakub.kicinski@...ronome.com, kvm@...r.kernel.org
Subject: Re: [RFC net-next v1 1/3] vfio/mdev: Inherit dma masks of parent
 device

On Fri,  8 Mar 2019 16:07:54 -0600
Parav Pandit <parav@...lanox.com> wrote:

> Inherit dma mask of parent device in child mdev devices, so that
> protocol stack can use right dma mask while doing dma mappings.
> 
> Signed-off-by: Parav Pandit <parav@...lanox.com>
> ---
>  drivers/vfio/mdev/mdev_core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index 0212f0e..9b8bdc9 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -315,6 +315,10 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid)
>  	mdev->dev.parent  = dev;
>  	mdev->dev.bus     = &mdev_bus_type;
>  	mdev->dev.release = mdev_device_release;
> +	mdev->dev.dma_mask = dev->dma_mask;
> +	mdev->dev.dma_parms = dev->dma_parms;
> +	mdev->dev.coherent_dma_mask = dev->coherent_dma_mask;
> +
>  	dev_set_name(&mdev->dev, "%pUl", uuid.b);
>  
>  	ret = device_register(&mdev->dev);

This seems like a rather large assumption and none of the existing mdev
drivers even make use of DMA ops.  Why shouldn't this be done in
mdev_parent_ops.create?  Thanks,

Alex