cxl/pci: Emit device serial number

Per the CXL specification (8.1.12.2 Memory Device PCIe Capabilities and
Extended Capabilities) the Device Serial Number capability is mandatory.
Emit it for user tooling to identify devices.

It is reasonable to ask whether the attribute should be added to the
list of PCI sysfs device attributes. The PCI layer can optionally emit
it too, but the CXL subsystem is aiming to preserve its independence and
the possibility of CXL topologies with non-PCI devices in it. To date
that has only proven useful for the 'cxl_test' model, but as can be seen
with seen with ACPI0016 devices, sometimes all that is needed is a
platform firmware table to point to CXL Component Registers in MMIO
space to define a "CXL" device.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/164366608838.196598.16856227191534267098.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/ABI/testing/sysfs-bus-cxl

@@ -25,6 +25,15 @@ Description:
 		identically named field in the Identify Memory Device Output
 		Payload in the CXL-2.0 specification.
 
+What:		/sys/bus/cxl/devices/memX/serial
+Date:		January, 2022
+KernelVersion:	v5.18
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) 64-bit serial number per the PCIe Device Serial Number
+		capability. Mandatory for CXL devices, see CXL 2.0 8.1.12.2
+		Memory Device PCIe Capabilities and Extended Capabilities.
+
 What:		/sys/bus/cxl/devices/*/devtype
 Date:		June, 2021
 KernelVersion:	v5.14

drivers/cxl/core/memdev.c

@@ -89,7 +89,18 @@ static ssize_t pmem_size_show(struct device *dev, struct device_attribute *attr,
 static struct device_attribute dev_attr_pmem_size =
 	__ATTR(size, 0444, pmem_size_show, NULL);
 
+static ssize_t serial_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+
+	return sysfs_emit(buf, "%#llx\n", cxlds->serial);
+}
+static DEVICE_ATTR_RO(serial);
+
 static struct attribute *cxl_memdev_attributes[] = {
+	&dev_attr_serial.attr,
 	&dev_attr_firmware_version.attr,
 	&dev_attr_payload_max.attr,
 	&dev_attr_label_storage_size.attr,

drivers/cxl/cxlmem.h

@@ -131,6 +131,7 @@ struct cxl_endpoint_dvsec_info {
  * @next_persistent_bytes: persistent capacity change pending device reset
  * @component_reg_phys: register base of component registers
  * @info: Cached DVSEC information about the device.
+ * @serial: PCIe Device Serial Number
  * @mbox_send: @dev specific transport for transmitting mailbox commands
  * @wait_media_ready: @dev specific method to await media ready
  *
@@ -164,6 +165,7 @@ struct cxl_dev_state {
 
 	resource_size_t component_reg_phys;
 	struct cxl_endpoint_dvsec_info info;
+	u64 serial;
 
 	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
 	int (*wait_media_ready)(struct cxl_dev_state *cxlds);

drivers/cxl/pci.c

@@ -567,6 +567,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (IS_ERR(cxlds))
 		return PTR_ERR(cxlds);
 
+	cxlds->serial = pci_get_dsn(pdev);
 	cxlds->cxl_dvsec = pci_find_dvsec_capability(
 		pdev, PCI_DVSEC_VENDOR_ID_CXL, CXL_DVSEC_PCIE_DEVICE);
 	if (!cxlds->cxl_dvsec)

tools/testing/cxl/test/mem.c

@@ -268,6 +268,7 @@ static int cxl_mock_mem_probe(struct platform_device *pdev)
 	if (IS_ERR(cxlds))
 		return PTR_ERR(cxlds);
 
+	cxlds->serial = pdev->id;
 	cxlds->mbox_send = cxl_mock_mbox_send;
 	cxlds->wait_media_ready = cxl_mock_wait_media_ready;
 	cxlds->payload_size = SZ_4K;