Subject: Re: [PATCH V2 mlx5-next 12/14] vfio/mlx5: Implement vfio_pci driver for mlx5 devices

From: Jason Gunthorpe <[email-masked]>
Date: Tue, 26 Oct 2021 12:25:24 -0300

On Tue, Oct 26, 2021 at 03:51:21PM +0100, Dr. David Alan Gilbert wrote:

> > It's more than asking nicely, we define the device_state bits as
> > synchronous, the device needs to enter the state before returning from
> > the write operation or return an errno.
> 
> I don't see how it can be synchronous in practice; can it really wait to
> complete if it has to take many cycles to finish off an inflight DMA
> before it transitions?

The fencing of outbound DMAs in the device must be synchronous, how
could anything work if it isn't?

Jason