powerpc/pseries/lparcfg: add missing RTAS retry status handling

The ibm,get-system-parameter RTAS function may return -2 or 990x,
which indicate that the caller should try again.

lparcfg's parse_system_parameter_string() ignores this, making it
possible to intermittently report incorrect SPLPAR characteristics.

Move the RTAS call into a coventional rtas_busy_delay()-based loop.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-4-26929c8cce78@linux.ibm.com

arch/powerpc/platforms/pseries/lparcfg.c

@@ -408,6 +408,7 @@ static void read_lpar_name(struct seq_file *m)
  */
 static void parse_system_parameter_string(struct seq_file *m)
 {
+	const s32 token = rtas_token("ibm,get-system-parameter");
 	int call_status;
 
 	unsigned char *local_buffer = kmalloc(SPLPAR_MAXLENGTH, GFP_KERNEL);
@@ -417,16 +418,15 @@ static void parse_system_parameter_string(struct seq_file *m)
 		return;
 	}
 
-	spin_lock(&rtas_data_buf_lock);
-	memset(rtas_data_buf, 0, SPLPAR_MAXLENGTH);
-	call_status = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
-				NULL,
-				SPLPAR_CHARACTERISTICS_TOKEN,
-				__pa(rtas_data_buf),
-				RTAS_DATA_BUF_SIZE);
-	memcpy(local_buffer, rtas_data_buf, SPLPAR_MAXLENGTH);
-	local_buffer[SPLPAR_MAXLENGTH - 1] = '\0';
-	spin_unlock(&rtas_data_buf_lock);
+	do {
+		spin_lock(&rtas_data_buf_lock);
+		memset(rtas_data_buf, 0, SPLPAR_MAXLENGTH);
+		call_status = rtas_call(token, 3, 1, NULL, SPLPAR_CHARACTERISTICS_TOKEN,
+					__pa(rtas_data_buf), RTAS_DATA_BUF_SIZE);
+		memcpy(local_buffer, rtas_data_buf, SPLPAR_MAXLENGTH);
+		local_buffer[SPLPAR_MAXLENGTH - 1] = '\0';
+		spin_unlock(&rtas_data_buf_lock);
+	} while (rtas_busy_delay(call_status));
 
 	if (call_status != 0) {
 		printk(KERN_INFO