Re: [PATCH v5 4/6] cxl/acpi: Add downstream port data to cxl_port instances

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

On Sat, 5 Jun 2021 23:05:17 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> In preparation for infrastructure that enumerates and configures the CXL
> decode mechanism of an upstream port to its downstream ports, add a
> representation for a CXL downstream port.
> 
> On ACPI systems the top-most logical downstream ports in the hierarchy
> are the host bridges (ACPI0016 devices) that decode the memory windows
> described by the CXL Early Discovery Table Fixed Memory Window
> Structures (CEDT.CFMWS).
> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |   13 ++++
>  drivers/cxl/acpi.c                      |   44 ++++++++++++++
>  drivers/cxl/core.c                      |   95 ++++++++++++++++++++++++++++++-
>  drivers/cxl/cxl.h                       |   21 +++++++
>  4 files changed, 169 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index fb996ced7629..0cb31b7ad17b 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -35,3 +35,16 @@ Description:
>  		CXL component registers. The 'uport' symlink connects the CXL
>  		portX object to the device that published the CXL port
>  		capability.
> +
> +What:		/sys/bus/cxl/devices/portX/dportY
> +Date:		June, 2021
> +KernelVersion:	v5.14
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		CXL port objects are enumerated from either a platform firmware
> +		device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
> +		CXL component registers. The 'dportY' symlink identifies one or
> +		more downstream ports that the upstream port may target in its
> +		decode of CXL memory resources.  The 'Y' integer reflects the
> +		hardware port unique-id used in the hardware decoder target
> +		list.
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 556d25ab6966..0ae7464b603d 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -5,19 +5,61 @@
>  #include <linux/device.h>
>  #include <linux/kernel.h>
>  #include <linux/acpi.h>
> +#include <linux/pci.h>

Not immediately seeing why this include is added in this patch.

>  #include "cxl.h"
>  
> +static struct acpi_device *to_cxl_host_bridge(struct device *dev)
> +{
> +	struct acpi_device *adev = to_acpi_device(dev);
> +
> +	if (strcmp(acpi_device_hid(adev), "ACPI0016") == 0)
> +		return adev;
> +	return NULL;
> +}
> +
> +static int add_host_bridge_dport(struct device *match, void *arg)
> +{
> +	int rc;
> +	acpi_status status;
> +	unsigned long long uid;
> +	struct cxl_port *root_port = arg;
> +	struct device *host = root_port->dev.parent;
> +	struct acpi_device *bridge = to_cxl_host_bridge(match);
> +
> +	if (!bridge)
> +		return 0;
> +
> +	status = acpi_evaluate_integer(bridge->handle, METHOD_NAME__UID, NULL,
> +				       &uid);
> +	if (status != AE_OK) {
> +		dev_err(host, "unable to retrieve _UID of %s\n",
> +			dev_name(match));
> +		return -ENODEV;
> +	}
> +
> +	rc = cxl_add_dport(root_port, match, uid, CXL_RESOURCE_NONE);
> +	if (rc) {
> +		dev_err(host, "failed to add downstream port: %s\n",
> +			dev_name(match));
> +		return rc;
> +	}
> +	dev_dbg(host, "add dport%llu: %s\n", uid, dev_name(match));
> +	return 0;
> +}
> +
>  static int cxl_acpi_probe(struct platform_device *pdev)
>  {
>  	struct cxl_port *root_port;
>  	struct device *host = &pdev->dev;
> +	struct acpi_device *adev = ACPI_COMPANION(host);
>  
>  	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
>  	if (IS_ERR(root_port))
>  		return PTR_ERR(root_port);
>  	dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
>  
> -	return 0;
> +	return bus_for_each_dev(adev->dev.bus, NULL, root_port,
> +				add_host_bridge_dport);
>  }
>  
>  static const struct acpi_device_id cxl_acpi_ids[] = {
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index dbbb34618d7d..4418b30cce4f 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -33,10 +33,22 @@ static struct attribute_group cxl_base_attribute_group = {
>  	.attrs = cxl_base_attributes,
>  };
>  
> +static void cxl_dport_release(struct cxl_dport *dport)
> +{
> +	put_device(dport->dport);
> +	list_del(&dport->list);
This ordering isn't the reverse of what happens cxl_add_dport()
That would be

list_del()
put_device()
kfree()

If there is a strong reason for that I'd like to see a comment here.

> +	kfree(dport);
> +}
> +
>  static void cxl_port_release(struct device *dev)
>  {
>  	struct cxl_port *port = to_cxl_port(dev);
> +	struct cxl_dport *dport, *_d;
>  
> +	device_lock(dev);
> +	list_for_each_entry_safe(dport, _d, &port->dports, list)
> +		cxl_dport_release(dport);
> +	device_unlock(dev);
>  	ida_free(&cxl_port_ida, port->id);
>  	kfree(port);
>  }
> @@ -60,9 +72,22 @@ struct cxl_port *to_cxl_port(struct device *dev)
>  	return container_of(dev, struct cxl_port, dev);
>  }
>  
> -static void unregister_dev(void *dev)
> +static void unregister_port(void *_port)
>  {
> -	device_unregister(dev);
> +	struct cxl_port *port = _port;
> +	struct cxl_dport *dport;
> +
> +	device_lock(&port->dev);
> +	list_for_each_entry(dport, &port->dports, list) {
> +		char link_name[CXL_TARGET_STRLEN];
> +
> +		if (snprintf(link_name, CXL_TARGET_STRLEN, "dport%d",
> +			     dport->port_id) >= CXL_TARGET_STRLEN)
> +			continue;
> +		sysfs_remove_link(&port->dev.kobj, link_name);
> +	}
> +	device_unlock(&port->dev);
> +	device_unregister(&port->dev);
>  }
>  
>  static void cxl_unlink_uport(void *_port)
> @@ -113,6 +138,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
>  
>  	port->uport = uport;
>  	port->component_reg_phys = component_reg_phys;
> +	INIT_LIST_HEAD(&port->dports);
>  
>  	device_initialize(dev);
>  	device_set_pm_not_required(dev);
> @@ -157,7 +183,7 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
>  	if (rc)
>  		goto err;
>  
> -	rc = devm_add_action_or_reset(host, unregister_dev, dev);
> +	rc = devm_add_action_or_reset(host, unregister_port, port);
>  	if (rc)
>  		return ERR_PTR(rc);
>  
> @@ -173,6 +199,69 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
>  }
>  EXPORT_SYMBOL_GPL(devm_cxl_add_port);
>  
> +static int add_dport(struct cxl_port *port, struct cxl_dport *new)
> +{
> +	struct cxl_dport *dport, *dup = NULL;
> +
> +	device_lock(&port->dev);
> +	list_for_each_entry (dport, &port->dports, list)
> +		if (new->port_id == dport->port_id) {
> +			dup = dport;
> +			goto err;
> +		}
> +	list_add_tail(&new->list, &port->dports);
> +	device_unlock(&port->dev);
> +
> +	return 0;
> +
> +err:
> +	device_unlock(&port->dev);
> +	dev_err(&port->dev,
> +		"unable to add dport%d-%s non-unique port id (%s)\n",
> +		new->port_id, dev_name(new->dport), dev_name(dup->dport));

As there is potential that you might end up with other errors in here long term,
why not move this to the point where the error is detected?
I think you are fine doing it under the mutex.  Obviously indent will be a deeper
than ideal.

> +	return -EEXIST;
> +}
> +
> +/*

This is a bit inconsistent wrt to what functions get full kernel-doc.
My personal preference would be all the exported functions + any others
where it is particularly useful.

> + * Append downstream port data to a cxl_port, note that all allocations
> + * and links are undone by cxl_port deletion and release.
> + */
> +int cxl_add_dport(struct cxl_port *port, struct device *dport_dev, int port_id,
> +		  resource_size_t component_reg_phys)
> +{
> +	char link_name[CXL_TARGET_STRLEN];
> +	struct cxl_dport *dport;
> +	int rc;
> +
> +	if (snprintf(link_name, CXL_TARGET_STRLEN, "dport%d", port_id) >=
> +	    CXL_TARGET_STRLEN)
> +		return -EINVAL;
> +
> +	dport = kzalloc(sizeof(*dport), GFP_KERNEL);
> +	if (!dport)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&dport->list);
> +	dport->dport = get_device(dport_dev);
> +	dport->port_id = port_id;
> +	dport->component_reg_phys = component_reg_phys;
> +	dport->port = port;
> +
> +	rc = add_dport(port, dport);
> +	if (rc)

If you get an error here, it's not been added to the list, but
in the cxl_dport_release() you remove it from the list. I think you 
just want to put and free the device here.


> +		goto err;
> +
> +	rc = sysfs_create_link(&port->dev.kobj, &dport_dev->kobj, link_name);
> +	if (rc)
> +		goto err;
> +
> +	return 0;
> +err:
> +	cxl_dport_release(dport);
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(cxl_add_dport);
> +
>  /**
>   * cxl_probe_component_regs() - Detect CXL Component register blocks
>   * @dev: Host device of the @base mapping
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 46c81165c210..0b89fcfe728a 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -146,6 +146,7 @@ int cxl_map_device_regs(struct pci_dev *pdev,
>  			struct cxl_register_map *map);
>  
>  #define CXL_RESOURCE_NONE ((resource_size_t) -1)
> +#define CXL_TARGET_STRLEN 20
>  
>  /**
>   * struct cxl_port - logical collection of upstream port devices and
> @@ -154,19 +155,39 @@ int cxl_map_device_regs(struct pci_dev *pdev,
>   * @dev: this port's device
>   * @uport: PCI or platform device implementing the upstream port capability
>   * @id: id for port device-name
> + * @dports: cxl_dport instances referenced by decoders
>   * @component_regs_phys: component register capability base address (optional)
>   */
>  struct cxl_port {
>  	struct device dev;
>  	struct device *uport;
>  	int id;
> +	struct list_head dports;
>  	resource_size_t component_reg_phys;
>  };
>  
> +/**
> + * struct cxl_dport - CXL downstream port
> + * @dport: PCI bridge or firmware device representing the downstream link
> + * @port_id: unique hardware identifier for dport in decoder target list
> + * @component_reg_phys: downstream port component registers
> + * @port: reference to cxl_port that contains this downstream port
> + * @list: node for a cxl_port's list of cxl_dport instances
> + */
> +struct cxl_dport {
> +	struct device *dport;
> +	int port_id;
> +	resource_size_t component_reg_phys;
> +	struct cxl_port *port;
> +	struct list_head list;
> +};
> +
>  struct cxl_port *to_cxl_port(struct device *dev);
>  struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
>  				   resource_size_t component_reg_phys,
>  				   struct cxl_port *parent_port);
>  
> +int cxl_add_dport(struct cxl_port *port, struct device *dport, int port_id,
> +		  resource_size_t component_reg_phys);
>  extern struct bus_type cxl_bus_type;
>  #endif /* __CXL_H__ */
>