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Message-ID: <6372dc26c8f2f_12cdff294e4@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 14 Nov 2022 16:24:06 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Robert Richter <rrichter@....com>,
Alison Schofield <alison.schofield@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>,
"Ira Weiny" <ira.weiny@...el.com>,
Ben Widawsky <bwidawsk@...nel.org>,
Dan Williams <dan.j.williams@...el.com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <lenb@...nel.org>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
"Davidlohr Bueso" <dave@...olabs.net>,
Dave Jiang <dave.jiang@...el.com>,
Robert Richter <rrichter@....com>
Subject: RE: [PATCH v3 4/9] cxl/mem: Skip intermediate port enumeration of
restricted endpoints (RCDs)
Robert Richter wrote:
> When an endpoint is found, all ports in beetween the endpoint and the
> CXL host bridge need to be created. In the RCH case there are no ports
> in between a host bridge and the endpoint. Skip the enumeration of
> intermediate ports.
>
> The port enumeration does not only create all ports, it also
> initializes the endpoint chain by adding the endpoint to every
> downstream port up to the root bridge. This must be done also in RCD
> mode, but is much more simple as the endpoint only needs to be added
> to the host bridge's dport.
>
> Note: For endpoint removal the cxl_detach_ep() is not needed as it is
> released in cxl_port_release().
>
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
> drivers/cxl/core/port.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index d10c3580719b..e21a9c3fe4da 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1366,8 +1366,24 @@ int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
> {
> struct device *dev = &cxlmd->dev;
> struct device *iter;
> + struct cxl_dport *dport;
> + struct cxl_port *port;
> int rc;
>
> + /*
> + * Skip intermediate port enumeration in the RCH case, there
> + * are no ports in between a host bridge and an endpoint. Only
> + * initialize the EP chain.
> + */
> + if (is_cxl_restricted(cxlmd)) {
> + port = cxl_mem_find_port(cxlmd, &dport);
> + if (!port)
> + return -ENXIO;
> + rc = cxl_add_ep(dport, &cxlmd->dev);
On second look, this seems problematic. While yes it will be deleted
when the root CXL port dies, it will not be deleted if the cxl_pci
driver is reloaded. I will code up a unit test to double check.
I note that cxl_add_ep() for the VH case is skipped for the root CXL
port, so I do not suspect it is needed here either. Did you add it for a
specific reason?
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