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Date:   Fri, 8 Jul 2022 07:57:10 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Matthew Wilcox <willy@infradead.org>
CC:     Bjorn Helgaas <helgaas@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-cxl@vger.kernel.org>,
        <linux-pci@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH 2/3] pci/doe: Use devm_xa_init()
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On Fri, Jul 08, 2022 at 03:49:51PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 08, 2022 at 07:45:12AM -0700, Ira Weiny wrote:
> > On Thu, Jul 07, 2022 at 11:06:46AM -0500, Bjorn Helgaas wrote:
> > > On Tue, Jul 05, 2022 at 04:21:58PM -0700, ira.weiny@intel.com wrote:
> > > > From: Ira Weiny <ira.weiny@intel.com>
> > > > 
> > > > The XArray being used to store the protocols does not even store
> > > > allocated objects.
> > > 
> > > I guess the point is that the doe_mb->prots XArray doesn't reference
> > > any other objects that would need to be freed when destroying
> > > doe_mb->prots?
> > 
> > Yes.
> > 
> > > A few more words here would make the commit log more
> > > useful to non-XArray experts.
> > 
> > I'll update this to be more clear in a V1 if it goes that far.  But to clarify
> > here; the protocol information is a u16 vendor id and u8 protocol number.  So
> > we are able to store that in the unsigned long value that would normally be a
> > pointer to something in the XArray.
> 
> Er.  Signed long.

Sorry I misspoke, xa_mk_value() takes an unsigned long.

> I can't find drivers/pci/doe.c in linux-next, so
> I have no idea if you're doing something wrong.

Sorry doe.c does not exist yet.  I came up with this idea while developing a
CXL series which is still in review.[0]

> But what you said here
> sounds wrong.

:-/

Can't I use xa_mk_value() to store data directly in the entry "pointer"?

From patch 3/9 in that series.[1]

+static void *pci_doe_xa_prot_entry(u16 vid, u8 prot)
+{
+	return xa_mk_value(((unsigned long)vid << 16) | prot);
+}

Both Dan and I thought this was acceptable in XArray?

Ira

[0] https://lore.kernel.org/linux-cxl/20220705154932.2141021-1-ira.weiny@intel.com/
[1] https://lore.kernel.org/linux-cxl/20220705154932.2141021-4-ira.weiny@intel.com/