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Date: Wed, 16 Jun 2021 09:08:16 -0700
From: Ben Widawsky <ben.widawsky@...el.com>
To: Alison Schofield <alison.schofield@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
Ira Weiny <ira.weiny@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>,
linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] cxl/acpi: Add the Host Bridge base address to CXL
port objects
On 21-06-15 17:20:38, Alison Schofield wrote:
> The base address for the Host Bridge port component registers is located
> in the CXL Host Bridge Structure (CHBS) of the ACPI CXL Early Discovery
> Table (CEDT). Retrieve the CHBS for each Host Bridge (ACPI0016 device)
> and include that base address in the port object.
>
> Co-developed-by: Vishal Verma <vishal.l.verma@...el.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> ---
> drivers/cxl/acpi.c | 105 ++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 99 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index be357eea552c..b6d9cd45428c 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -8,6 +8,61 @@
> #include <linux/pci.h>
> #include "cxl.h"
>
> +static struct acpi_table_header *cedt_table;
cedt_header would really be a better name. "Table" is redundant as the 't' in
CEDT is table.
> +
> +static struct acpi_cedt_chbs *cxl_acpi_match_chbs(struct device *dev, u32 uid)
> +{
> + struct acpi_cedt_chbs *chbs, *chbs_match = NULL;
> + acpi_size len, cur = 0;
> + void *cedt_base;
maybe "cedt_body", or "cedt_subtables"
> + int rc = 0;
> +
> + len = cedt_table->length - sizeof(*cedt_table);
> + cedt_base = cedt_table + 1;
As per naming recommendation above, this looks really funny...
> +
> + while (cur < len) {
> + struct acpi_cedt_header *c = cedt_base + cur;
Okay, now I see why you may have not called the previous thing a header.
> +
> + if (c->type != ACPI_CEDT_TYPE_CHBS) {
> + cur += c->length;
> + continue;
> + }
> +
> + chbs = cedt_base + cur;
> +
> + if (chbs->header.length < sizeof(*chbs)) {
> + dev_err(dev, "Invalid CHBS header length: %u\n",
> + chbs->header.length);
> + rc = -EINVAL;
> + break;
> + }
I'd just continue here. Maybe there will be another chbs with the correct size.
> +
> + if (chbs->uid == uid && !chbs_match) {
> + chbs_match = chbs;
> + cur += c->length;
> + continue;
> + }
> +
> + if (chbs->uid == uid && chbs_match) {
> + dev_err(dev, "Duplicate CHBS UIDs %u\n", uid);
> + rc = -EINVAL;
> + break;
> + }
I'd also just continue here. I think if we have a match, we can just use it and
ignore BIOS bugs. I'd probably write it like this:
if (chbs->uid == uid) {
dev_WARN_ONCE(dev, chbs_match, "Duplicate CHBS UIDs %u\n", uid);
chbs_match = chbs; /* last one wins */
cur += c->length;
continue;
}
Up to you how you actually write it, but do consider not failing here.
> + cur += c->length;
> + }
> + if (!chbs_match)
> + rc = -EINVAL;
Maybe ENODEV or something like it is more appropriate?
> + if (rc)
> + return ERR_PTR(rc);
> +
> + return chbs_match;
> +}
> +
> +static resource_size_t get_chbcr(struct acpi_cedt_chbs *chbs)
> +{
> + return IS_ERR(chbs) ? CXL_RESOURCE_NONE : chbs->base;
> +}
> +
> struct cxl_walk_context {
> struct device *dev;
> struct pci_bus *root;
> @@ -50,6 +105,21 @@ static int match_add_root_ports(struct pci_dev *pdev, void *data)
> return 0;
> }
>
> +static struct cxl_dport *find_dport_by_dev(struct cxl_port *port, struct device *dev)
> +{
> + struct cxl_dport *dport;
> +
> + device_lock(&port->dev);
> + list_for_each_entry(dport, &port->dports, list)
> + if (dport->dport == dev) {
> + device_unlock(&port->dev);
> + return dport;
> + }
> +
> + device_unlock(&port->dev);
> + return NULL;
> +}
> +
> static struct acpi_device *to_cxl_host_bridge(struct device *dev)
> {
> struct acpi_device *adev = to_acpi_device(dev);
> @@ -71,6 +141,7 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> struct acpi_pci_root *pci_root;
> struct cxl_walk_context ctx;
> struct cxl_decoder *cxld;
> + struct cxl_dport *dport;
> struct cxl_port *port;
>
> if (!bridge)
> @@ -80,8 +151,15 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> if (!pci_root)
> return -ENXIO;
>
> - /* TODO: fold in CEDT.CHBS retrieval */
> - port = devm_cxl_add_port(host, match, CXL_RESOURCE_NONE, root_port);
> + dport = find_dport_by_dev(root_port, match);
> + if (!dport) {
> + dev_dbg(host, "host bridge expected and not found\n");
> + return -ENODEV;
> + }
> +
> + port = devm_cxl_add_port(host, match, dport->component_reg_phys,
> + root_port);
> +
> if (IS_ERR(port))
> return PTR_ERR(port);
> dev_dbg(host, "%s: add: %s\n", dev_name(match), dev_name(&port->dev));
> @@ -120,6 +198,7 @@ static int add_host_bridge_dport(struct device *match, void *arg)
> int rc;
> acpi_status status;
> unsigned long long uid;
> + struct acpi_cedt_chbs *chbs;
> struct cxl_port *root_port = arg;
> struct device *host = root_port->dev.parent;
> struct acpi_device *bridge = to_cxl_host_bridge(match);
> @@ -135,7 +214,12 @@ static int add_host_bridge_dport(struct device *match, void *arg)
> return -ENODEV;
> }
>
> - rc = cxl_add_dport(root_port, match, uid, CXL_RESOURCE_NONE);
> + chbs = cxl_acpi_match_chbs(host, uid);
> + if (IS_ERR(chbs))
> + dev_dbg(host, "No CHBS found for Host Bridge: %s\n",
> + dev_name(match));
> +
> + rc = cxl_add_dport(root_port, match, uid, get_chbcr(chbs));
> if (rc) {
> dev_err(host, "failed to add downstream port: %s\n",
> dev_name(match));
> @@ -148,6 +232,7 @@ static int add_host_bridge_dport(struct device *match, void *arg)
> static int cxl_acpi_probe(struct platform_device *pdev)
> {
> int rc;
> + acpi_status status;
> struct cxl_port *root_port;
> struct device *host = &pdev->dev;
> struct acpi_device *adev = ACPI_COMPANION(host);
> @@ -157,17 +242,25 @@ static int cxl_acpi_probe(struct platform_device *pdev)
> return PTR_ERR(root_port);
> dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
>
> + status = acpi_get_table(ACPI_SIG_CEDT, 0, &cedt_table);
> + if (ACPI_FAILURE(status))
> + return -ENXIO;
> +
> rc = bus_for_each_dev(adev->dev.bus, NULL, root_port,
> add_host_bridge_dport);
> if (rc)
> - return rc;
> + goto out;
>
> /*
> * Root level scanned with host-bridge as dports, now scan host-bridges
> * for their role as CXL uports to their CXL-capable PCIe Root Ports.
> */
> - return bus_for_each_dev(adev->dev.bus, NULL, root_port,
> - add_host_bridge_uport);
> + rc = bus_for_each_dev(adev->dev.bus, NULL, root_port,
> + add_host_bridge_uport);
> +
> +out:
> + acpi_put_table(cedt_table);
> + return rc;
> }
>
> static const struct acpi_device_id cxl_acpi_ids[] = {
> --
> 2.26.2
>
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