linux-kernel - Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver

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Date:   Wed, 22 Jul 2020 15:16:30 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     "Dey, Megha" <megha.dey@...el.com>
Cc:     Dave Jiang <dave.jiang@...el.com>, vkoul@...nel.org,
        maz@...nel.org, bhelgaas@...gle.com, rafael@...nel.org,
        gregkh@...uxfoundation.org, tglx@...utronix.de, hpa@...or.com,
        alex.williamson@...hat.com, jacob.jun.pan@...el.com,
        ashok.raj@...el.com, yi.l.liu@...el.com, baolu.lu@...el.com,
        kevin.tian@...el.com, sanjay.k.kumar@...el.com,
        tony.luck@...el.com, jing.lin@...el.com, dan.j.williams@...el.com,
        kwankhede@...dia.com, eric.auger@...hat.com, parav@...lanox.com,
        dave.hansen@...el.com, netanelg@...lanox.com, shahafs@...lanox.com,
        yan.y.zhao@...ux.intel.com, pbonzini@...hat.com,
        samuel.ortiz@...el.com, mona.hossain@...el.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-pci@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and
 DEV-MSI support for the idxd driver

On Wed, Jul 22, 2020 at 10:31:28AM -0700, Dey, Megha wrote:
> > > I didn't notice any of this in the patch series? What is the calling
> > > context for the platform_msi_ops ? I think I already mentioned that
> > > ideally we'd need blocking/sleeping. The big selling point is that IMS
> > > allows this data to move off-chip, which means accessing it is no
> > > longer just an atomic write to some on-chip memory.
> > > 
> > > These details should be documented in the comment on top of
> > > platform_msi_ops
> 
> so the platform_msi_ops care called from the same context as the existing
> msi_ops for instance, we are not adding anything new. I think the above
> comment is a little misleading I will remove it next time around.

If it is true that all calls are under driver control then I think it
would be good to document that. I actually don't know off hand if
mask/unmask are restricted like that

As this is a op a driver has to implement vs the arch it probably need
a bit more hand holding.

> Also, I thought even the current write to on-chip memory is not
> atomic..

The writel to the MSI-X table in MMIO memory is 'atomic'

Jason