linux-kernel - Re: [RFC PATCH 2/4] mdev: introduce helper to set per device dma ops

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Message-ID: <20190917130044.4fb97637@x1.home>
Date:   Tue, 17 Sep 2019 13:00:44 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kwankhede@...dia.com,
        cohuck@...hat.com, tiwei.bie@...el.com, maxime.coquelin@...hat.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        rob.miller@...adcom.com, idos@...lanox.com, xiao.w.wang@...el.com,
        haotian.wang@...ive.com
Subject: Re: [RFC PATCH 2/4] mdev: introduce helper to set per device dma
 ops

On Tue, 10 Sep 2019 16:19:33 +0800
Jason Wang <jasowang@...hat.com> wrote:

> This patch introduces mdev_set_dma_ops() which allows parent to set
> per device DMA ops. This help for the kernel driver to setup a correct
> DMA mappings.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vfio/mdev/mdev_core.c | 7 +++++++
>  include/linux/mdev.h          | 2 ++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index b558d4cfd082..eb28552082d7 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -13,6 +13,7 @@
>  #include <linux/uuid.h>
>  #include <linux/sysfs.h>
>  #include <linux/mdev.h>
> +#include <linux/dma-mapping.h>
>  
>  #include "mdev_private.h"
>  
> @@ -27,6 +28,12 @@ static struct class_compat *mdev_bus_compat_class;
>  static LIST_HEAD(mdev_list);
>  static DEFINE_MUTEX(mdev_list_lock);
>  
> +void mdev_set_dma_ops(struct mdev_device *mdev, struct dma_map_ops *ops)
> +{
> +	set_dma_ops(&mdev->dev, ops);
> +}
> +EXPORT_SYMBOL(mdev_set_dma_ops);
> +

Why does mdev need to be involved here?  Your sample driver in 4/4 calls
this from its create callback, where it could just as easily call:

  set_dma_ops(mdev_dev(mdev), ops);

Thanks,
Alex

>  struct device *mdev_parent_dev(struct mdev_device *mdev)
>  {
>  	return mdev->parent->dev;
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 0ce30ca78db0..7195f40bf8bf 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -145,4 +145,6 @@ struct device *mdev_parent_dev(struct mdev_device *mdev);
>  struct device *mdev_dev(struct mdev_device *mdev);
>  struct mdev_device *mdev_from_dev(struct device *dev);
>  
> +void mdev_set_dma_ops(struct mdev_device *mdev, struct dma_map_ops *ops);
> +
>  #endif /* MDEV_H */