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Message-ID: <20211025122938.GR2744544@nvidia.com>
Date: Mon, 25 Oct 2021 09:29:38 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: Cornelia Huck <cohuck@...hat.com>,
Yishai Hadas <yishaih@...dia.com>, bhelgaas@...gle.com,
saeedm@...dia.com, linux-pci@...r.kernel.org, kvm@...r.kernel.org,
netdev@...r.kernel.org, kuba@...nel.org, leonro@...dia.com,
kwankhede@...dia.com, mgurtovoy@...dia.com, maorg@...dia.com,
"Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH V2 mlx5-next 12/14] vfio/mlx5: Implement vfio_pci driver
for mlx5 devices
On Thu, Oct 21, 2021 at 03:47:29PM -0600, Alex Williamson wrote:
> I recall that we previously suggested a very strict interpretation of
> clearing the _RUNNING bit, but again I'm questioning if that's a real
> requirement or simply a nice-to-have feature for some undefined
> debugging capability. In raising the p2p DMA issue, we can see that a
> hard stop independent of other devices is not really practical but I
> also don't see that introducing a new state bit solves this problem any
> more elegantly than proposed here. Thanks,
I still disagree with this - the level of 'frozenness' of a device is
something that belongs in the defined state exposed to userspace, not
as a hidden internal state that userspace can't see.
It makes the state transitions asymmetric between suspend/resume as
resume does have a defined uAPI state for each level of frozeness and
suspend does not.
With the extra bit resume does:
0000, 0100, 1000, 0001
And suspend does:
0001, 1001, 0010, 0000
However, without the extra bit suspend is only
001, 010, 000
With hidden state inside the 010
Jason
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