linux-kernel - Re: [PATCH V11 3/8] PCI: Create PCI library functions in support of DOE mailboxes.

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Date:   Thu, 23 Jun 2022 11:03:02 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ira Weiny <ira.weiny@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alison Schofield <alison.schofield@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Ben Widawsky" <bwidawsk@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V11 3/8] PCI: Create PCI library functions in support of
 DOE mailboxes.

Ira Weiny wrote:
> On Mon, Jun 20, 2022 at 11:23:28AM +0100, Jonathan Cameron wrote:
> > On Fri, 17 Jun 2022 15:56:38 -0700
> > Dan Williams <dan.j.williams@...el.com> wrote:
> > 
> 
> [snip]
> 
> > > > +static int pci_doe_enable_irq(struct pci_doe_mb *doe_mb, unsigned int irq)
> > > > +{
> > > > +	struct pci_dev *pdev = doe_mb->pdev;
> > > > +	int offset = doe_mb->cap_offset;
> > > > +	int rc;
> > > > +
> > > > +	/*
> > > > +	 * Enabling bus mastering is required for MSI/MSIx.  It is safe to call
> > > > +	 * this multiple times and thus is called here to ensure that mastering
> > > > +	 * is enabled even if the driver has done so.
> > > > +	 */  
> > > 
> > > It is required for MSI/MSIx to work, yes, but if the caller that created
> > > the doe object has not set it yet that's its prerogative.
> > 
> > We went around this in one of the earlier threads, and I think consensus
> > was that it made sense to have this in core code.
> 
> Yes we did.  This is where Bjorn asked for this to be done I thought.
> 
> I verified that pci_set_master() is fine to call more than one time.  If the
> caller asks for irq support I think it is fine to do this here to ensure that
> support is enabled.

Its moot now that irq support is being pushed out to a follow-on
change, but I think its unfortunate that this makes it difficult to
audit when and where a device will be enabled to send cycles. If at all
possible I think it makes sense to keep this the responsibility of the
driver for the pci_dev. Similar to how pcie_port_device_register() does
this on behalf of the services it registers rather than each service
doing this itself.