Re: [PATCH 2/2] virtio: Add polling virtio-mmio device reset completion

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Sep 22, 2024 at 08:34:35PM +0800, Jianguo Sun wrote:
> We write 0 to device_status to initiate reset of a virtio-mmio device.
> The reset operation itself may or may not be completed by the time
> write instruction completes. Add polling device_status to return
> 0 to ensure reset completion before reinitializing the device.
> 
> Change-Id: If15d11d090dfd0d4972ad35f49af03e076872413
> Signed-off-by: Jianguo Sun <quic_jianguos@quicinc.com>
> Signed-off-by: Sreenad Menon <quic_sreemeno@quicinc.com>
> Signed-off-by: Anant Goel <quic_anantg@quicinc.com>
> ---
>  drivers/virtio/virtio_mmio.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 90e784e7b721..c34ad1782145 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -70,6 +70,7 @@
>  #include <linux/virtio_config.h>
>  #include <uapi/linux/virtio_mmio.h>
>  #include <linux/virtio_ring.h>
> +#include <linux/delay.h>
>  
>  
>  
> @@ -269,6 +270,13 @@ static void vm_reset(struct virtio_device *vdev)
>  
>  	/* 0 status means a reset. */
>  	writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
> +#ifdef CONFIG_VIRTIO_MMIO_POLL_RESET
> +	/* After writing 0 to device_status, the driver MUST wait for a read of
> +	 * device_status to return 0 before reinitializing the device.
> +	 */

This is not in the spec, is it? First you need a spec patch. Then implement it.


> +	while (readl(vm_dev->base + VIRTIO_MMIO_STATUS))
> +		usleep_range(1000, 1100);
> +#endif
>  }
>  
>  
> -- 
> 2.17.1