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

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Date:   Fri, 25 Sep 2020 14:16:41 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sherry Sun <sherry.sun@....com>
Cc:     sudeep.dutt@...el.com, ashutosh.dixit@...el.com, arnd@...db.de,
        wang.yi59@....com.cn, huang.zijiang@....com.cn,
        rikard.falkeborn@...il.com, lee.jones@...aro.org, mst@...hat.com,
        linux-kernel@...r.kernel.org, linux-imx@....com
Subject: Re: [PATCH 4/5] misc: vop: set VIRTIO_F_ACCESS_PLATFORM for
 nocoherent platform

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.
> 
> Signed-off-by: Sherry Sun <sherry.sun@....com>
> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> ---
>  drivers/misc/mic/vop/vop_main.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/misc/mic/vop/vop_main.c b/drivers/misc/mic/vop/vop_main.c
> index d3645122c983..d609f0dc6124 100644
> --- a/drivers/misc/mic/vop/vop_main.c
> +++ b/drivers/misc/mic/vop/vop_main.c
> @@ -125,6 +125,9 @@ static void vop_transport_features(struct virtio_device *vdev)
>  	 * creates virtio rings on preallocated memory.
>  	 */
>  	__virtio_clear_bit(vdev, VIRTIO_F_RING_PACKED);
> +
> +	if (!dev_is_dma_coherent(vdev->dev.parent))
> +		__virtio_set_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);

Why look at the parent and not the device itself?