RE: [PATCH v5 1/3] CXL, PCIE: Add cxl_rcrb_addr file to dport_dev

[Dan Williams <dan.j.williams@intel.com>]

Ben Cheatham wrote:
> Add cxl_rcrb_addr to the dport_dev (normally represented by a pcie
> device) for CXL RCH root ports. The file will print the RCRB base
> MMIO address of the root port when read and will be used by
> users looking to inject CXL EINJ error types for RCH hosts.

RCRB is an implementation detail of RCH topologies, I don't see why
userspace needs this information, maybe it becomes clearer in the follow
on patches, but I would hope this detail could be hidden.

> Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |  9 ++++
>  drivers/cxl/acpi.c                      |  2 +
>  drivers/cxl/core/port.c                 | 58 +++++++++++++++++++++++++
>  drivers/cxl/cxl.h                       |  2 +
>  4 files changed, 71 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 087f762ebfd5..85621da69296 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -177,6 +177,15 @@ Description:
>  		integer reflects the hardware port unique-id used in the
>  		hardware decoder target list.
>  
> +What:		/sys/bus/cxl/devices/portX/dportY/cxl_rcrb_addr
> +What:		/sys/devices/pciX/cxl_rcrb_addr
> +Date:		August, 2023
> +KernelVersion:	v6.6
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) The 'cxl_rcrb_addr' device file gives the MMIO base address
> +		of the RCRB of the corresponding CXL 1.1 downstream port. Only
> +		present for CXL 1.1 dports.
>  
>  What:		/sys/bus/cxl/devices/decoderX.Y
>  Date:		June, 2021
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index d1c559879dcc..3e2ca946bf47 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -676,6 +676,8 @@ static int cxl_acpi_probe(struct platform_device *pdev)
>  	if (IS_ERR(root_port))
>  		return PTR_ERR(root_port);
>  
> +	set_cxl_root(root_port);
> +

The cxl_root is not a singleton and the way to determine this linkage is
by walking up the port hierarchy. See find_cxl_root().

>  	rc = bus_for_each_dev(adev->dev.bus, NULL, root_port,
>  			      add_host_bridge_dport);
>  	if (rc < 0)
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 724be8448eb4..c3914e73f67e 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -875,6 +875,14 @@ struct cxl_port *find_cxl_root(struct cxl_port *port)
>  }
>  EXPORT_SYMBOL_NS_GPL(find_cxl_root, CXL);
>  
> +static struct cxl_port *cxl_root;
> +
> +void set_cxl_root(struct cxl_port *root_port)
> +{
> +	cxl_root = root_port;
> +}
> +EXPORT_SYMBOL_NS_GPL(set_cxl_root, CXL);
> +
>  static struct cxl_dport *find_dport(struct cxl_port *port, int id)
>  {
>  	struct cxl_dport *dport;
> @@ -930,11 +938,56 @@ static void cond_cxl_root_unlock(struct cxl_port *port)
>  		device_unlock(&port->dev);
>  }
>  
> +static ssize_t cxl_rcrb_addr_show(struct device *dev,
> +				  struct device_attribute *attr, char *buf)
> +{
> +	struct cxl_dport *dport;
> +
> +	if (!cxl_root)
> +		return -ENODEV;
> +
> +	dport = cxl_find_dport_by_dev(cxl_root, dev);
> +	if (!dport)
> +		return -ENODEV;
> +
> +	return sysfs_emit(buf, "0x%llx\n", (u64) dport->rcrb.base);
> +}
> +DEVICE_ATTR_RO(cxl_rcrb_addr);
> +
> +static umode_t cxl_rcrb_addr_is_visible(struct kobject *kobj,
> +					struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cxl_dport *dport;
> +
> +	if (!IS_ENABLED(CONFIG_ACPI_APEI_EINJ) || !cxl_root)
> +		return 0;
> +
> +	dport = cxl_find_dport_by_dev(cxl_root, dev);
> +	if (!dport || !dport->rch || dport->rcrb.base == CXL_RESOURCE_NONE)
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +static struct attribute *cxl_rcrb_addr_attrs[] = {
> +	&dev_attr_cxl_rcrb_addr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group cxl_rcrb_addr_group = {
> +	.attrs = cxl_rcrb_addr_attrs,
> +	.is_visible = cxl_rcrb_addr_is_visible,
> +};
> +
>  static void cxl_dport_remove(void *data)
>  {
>  	struct cxl_dport *dport = data;
>  	struct cxl_port *port = dport->port;
>  
> +	if (dport->rch)
> +		sysfs_remove_group(&dport->dport_dev->kobj, &cxl_rcrb_addr_group);
> +
>  	xa_erase(&port->dports, (unsigned long) dport->dport_dev);
>  	put_device(dport->dport_dev);
>  }
> @@ -1021,6 +1074,11 @@ __devm_cxl_add_dport(struct cxl_port *port, struct device *dport_dev,
>  	if (rc)
>  		return ERR_PTR(rc);
>  
> +	rc = sysfs_create_group(&dport_dev->kobj, &cxl_rcrb_addr_group);
> +	if (rc)
> +		dev_dbg(dport_dev, "Couldn't create cxl_rcrb_addr group: %d\n",
> +			rc);

Please no dynamic sysfs attribute registration. If this attribute is
needed it should be static.