Re: [PATCH v2 1/2] cxl/acpi: Add the Host Bridge base address to CXL port objects

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 15 Jun 2021 17:20:38 -0700
Alison Schofield <alison.schofield@intel.com> 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@intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>

Hi Alison,

A few small suggestions from me.

> ---
>  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;
> +
> +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;
> +	int rc = 0;
> +
> +	len = cedt_table->length - sizeof(*cedt_table);
> +	cedt_base = cedt_table + 1;
> +
> +	while (cur < len) {
> +		struct acpi_cedt_header *c = cedt_base + cur;
> +
> +		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;

As below, direct return would be more obvious to my eyes.

> +			break;
> +		}
> +
> +		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);

Do we actually care, or should we just drop out on first match?
I don't think think there is any obligation to catch broken tables.

> +			rc = -EINVAL;

Direct return might be easier to follow.
			return ERR_PTR(-EINVAL);

> +			break;
> +		}

Maybe more readable as (your option is fine if you prefer it).

		if (chbs->uuid != uid) {
			cur += c->length;
			continue;
		}

		if (chbs_match) {
			dev_err(dev, "D...");
			return ERR_PTR(-EINVAL);
		}

		chbs_match = chbs;


> +		cur += c->length;
> +	}
> +	if (!chbs_match)
> +		rc = -EINVAL;

		return ERR_PTR(-EINVAL);

> +	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);
> +

Nitpick, no blank line before error handling block.

>  	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[] = {