linux-kernel - Re: [PATCH V10 5/9] cxl/port: Find a DOE mailbox which supports CDAT

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Date:   Wed, 8 Jun 2022 14:38:35 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Ben Widawsky <bwidawsk@...nel.org>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        "Alison Schofield" <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V10 5/9] cxl/port: Find a DOE mailbox which supports CDAT

On Wed, Jun 08, 2022 at 12:39:49PM -0700, Ira wrote:
> On Mon, Jun 06, 2022 at 10:48:19AM -0700, Ben Widawsky wrote:
> > On 22-06-04 17:50:45, ira.weiny@...el.com wrote:
> > > From: Ira Weiny <ira.weiny@...el.com>
> > > 

[snip]

> > > +
> > > +/**
> > > + * cxl_cache_cdat_mb() -- cache the DOE mailbox which suports the CDAT protocol
> > > + *
> > > + * @port: Port to containing DOE Mailboxes
> > > + *
> > > + * Cache a pointer to the doe mailbox which supports CDAT.
> > > + */
> > > +void cxl_cache_cdat_mb(struct cxl_port *port)
> > > +{
> > > +	struct device *dev = port->uport;
> > > +	struct cxl_memdev *cxlmd;
> > > +	struct cxl_dev_state *cxlds;
> > > +	int i;
> > > +
> > > +	if (!is_cxl_memdev(dev))
> > > +		return;
> > > +
> > > +	cxlmd = to_cxl_memdev(dev);
> > > +	cxlds = cxlmd->cxlds;
> > > +
> > > +	for (i = 0; i < cxlds->num_mbs; i++) {
> > > +		struct pci_doe_mb *cur = cxlds->doe_mbs[i];
> > > +
> > > +		if (pci_doe_supports_prot(cur, PCI_DVSEC_VENDOR_ID_CXL,
> > > +					  CXL_DOE_PROTOCOL_TABLE_ACCESS)) {
> > > +			port->cdat_mb = cur;
> > 
> > What happens if cxl_pci is unloaded after this? Would it be better to copy out
> > the CDAT info? Otherwise, I think you need to hold a ref on the PCI device
> > (though I only took a quick look).
> 
> <sigh> I thought that could not happen but I see I was wrong.
> 
> A reference will need to be taken for at least the duration of the query.
> Originally I had this set up to try and make it easier to query later.  But I
> think that is a waste ATM.
> 
> I'm going to rework this ownership.

BTW this means this patch is going away.  I think just searching for the
mailbox with CDAT support on each query is the way to go at this time.

Ira

> 
> Thanks for the review,
> Ira
>