linux-kernel - Re: [PATCH] PCI/DOE: Remove asynchronous task support

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Message-ID: <20221122194829.GB20515@wunner.de>
Date:   Tue, 22 Nov 2022 20:48:29 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Gregory Price <gregory.price@...verge.com>,
        "Li, Ming4" <ming4.li@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        "Schofield, Alison" <alison.schofield@...el.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI/DOE: Remove asynchronous task support

On Mon, Nov 21, 2022 at 05:41:48PM +0000, Jonathan Cameron wrote:
> On Mon, 21 Nov 2022 14:17:37 +0000 "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com> wrote:
> > It's good that this potential issue has been noticed. I think moving
> > the 'find' logic and the xarray from CXL to the PCI core should save
> > a lot of such duplicated works for other drivers using DOE.
> > 
> > One more though:
> > For a driver, I think it's only interested in getting a DOE mailbox
> > from a PCI device with specified VID+protocol and using it.
> > The driver doesn't care how is the DOE mailbox instance created and
> > the driver also doesn't want to maintain it.

Totally agree on all of your above points Qiuxu.


> > After using the DOE mailbox instance then the driver puts it back.

That won't be necessary I think.  The PCI core allocates all existing
DOE mailboxes and enumerates the supported protocols.  Drivers just
ask the PCI core for a mailbox supporting a specific protocol and
are free to use that as long as the PCI device exists.


> There is also a dance around interrupts (once those are supported
> for DOEs in general).  Until the PCI driver has requested interrupts
> we can't use them for DOE, but we may want to poll it before that
> stage then switch over.

Thomas Gleixner has returned to his patch sets for dynamic MSI-X
allocation.  We'll be able to leverage that to request an interrupt
in the PCI core for DOE before a driver is bound.  And a driver
can then get additional MSI-X vectors if needed.  Will only work
for MSI-X though, not MSI.

Thanks,

Lukas