powerpc/pseries: read the lpar name from the firmware

The LPAR name may be changed after the LPAR has been started in the HMC.
In that case lparstat command is not reporting the updated value because
it reads it from the device tree which is read at boot time.

However this value could be read from RTAS.

Adding this value in the /proc/powerpc/lparcfg output allows to read the
updated value.

However the hypervisor, like Qemu/KVM, may not support this RTAS
parameter. In that case the value reported in lparcfg is read from the
device tree and so is not updated accordingly.
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com>
[mpe: Drop doc-comment syntax, change RTAS/DT to lower case, use of_root
      to fix missing of_node_put(), use of_property_read_string()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220106161339.74656-1-ldufour@linux.ibm.com

arch/powerpc/platforms/pseries/lparcfg.c

@@ -311,6 +311,92 @@ static void parse_mpp_x_data(struct seq_file *m)
 		seq_printf(m, "coalesce_pool_spurr=%ld\n", mpp_x_data.pool_spurr_cycles);
 }
 
+/*
+ * PAPR defines, in section "7.3.16 System Parameters Option", the token 55 to
+ * read the LPAR name, and the largest output data to 4000 + 2 bytes length.
+ */
+#define SPLPAR_LPAR_NAME_TOKEN	55
+#define GET_SYS_PARM_BUF_SIZE	4002
+#if GET_SYS_PARM_BUF_SIZE > RTAS_DATA_BUF_SIZE
+#error "GET_SYS_PARM_BUF_SIZE is larger than RTAS_DATA_BUF_SIZE"
+#endif
+
+/*
+ * Read the lpar name using the RTAS ibm,get-system-parameter call.
+ *
+ * The name read through this call is updated if changes are made by the end
+ * user on the hypervisor side.
+ *
+ * Some hypervisor (like Qemu) may not provide this value. In that case, a non
+ * null value is returned.
+ */
+static int read_rtas_lpar_name(struct seq_file *m)
+{
+	int rc, len, token;
+	union {
+		char raw_buffer[GET_SYS_PARM_BUF_SIZE];
+		struct {
+			__be16 len;
+			char name[GET_SYS_PARM_BUF_SIZE-2];
+		};
+	} *local_buffer;
+
+	token = rtas_token("ibm,get-system-parameter");
+	if (token == RTAS_UNKNOWN_SERVICE)
+		return -EINVAL;
+
+	local_buffer = kmalloc(sizeof(*local_buffer), GFP_KERNEL);
+	if (!local_buffer)
+		return -ENOMEM;
+
+	do {
+		spin_lock(&rtas_data_buf_lock);
+		memset(rtas_data_buf, 0, sizeof(*local_buffer));
+		rc = rtas_call(token, 3, 1, NULL, SPLPAR_LPAR_NAME_TOKEN,
+			       __pa(rtas_data_buf), sizeof(*local_buffer));
+		if (!rc)
+			memcpy(local_buffer->raw_buffer, rtas_data_buf,
+			       sizeof(local_buffer->raw_buffer));
+		spin_unlock(&rtas_data_buf_lock);
+	} while (rtas_busy_delay(rc));
+
+	if (!rc) {
+		/* Force end of string */
+		len = min((int) be16_to_cpu(local_buffer->len),
+			  (int) sizeof(local_buffer->name)-1);
+		local_buffer->name[len] = '\0';
+
+		seq_printf(m, "partition_name=%s\n", local_buffer->name);
+	} else
+		rc = -ENODATA;
+
+	kfree(local_buffer);
+	return rc;
+}
+
+/*
+ * Read the LPAR name from the Device Tree.
+ *
+ * The value read in the DT is not updated if the end-user is touching the LPAR
+ * name on the hypervisor side.
+ */
+static int read_dt_lpar_name(struct seq_file *m)
+{
+	const char *name;
+
+	if (of_property_read_string(of_root, "ibm,partition-name", &name))
+		return -ENOENT;
+
+	seq_printf(m, "partition_name=%s\n", name);
+	return 0;
+}
+
+static void read_lpar_name(struct seq_file *m)
+{
+	if (read_rtas_lpar_name(m) && read_dt_lpar_name(m))
+		pr_err_once("Error can't get the LPAR name");
+}
+
 #define SPLPAR_CHARACTERISTICS_TOKEN 20
 #define SPLPAR_MAXLENGTH 1026*(sizeof(char))
 
@@ -496,6 +582,7 @@ static int pseries_lparcfg_data(struct seq_file *m, void *v)
 
 	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
 		/* this call handles the ibm,get-system-parameter contents */
+		read_lpar_name(m);
 		parse_system_parameter_string(m);
 		parse_ppp_data(m);
 		parse_mpp_data(m);