powerpc/pseries/setup: 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.

pSeries_cmo_feature_init() ignores this, making it possible to fail to
detect cooperative memory overcommit capabilities during boot.

Move the RTAS call into a conventional rtas_busy_delay()-based
loop, dropping unnecessary clearing of rtas_data_buf.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-5-26929c8cce78@linux.ibm.com

arch/powerpc/platforms/pseries/setup.c

@@ -941,21 +941,25 @@ void pSeries_coalesce_init(void)
  */
 static void __init pSeries_cmo_feature_init(void)
 {
+	const s32 token = rtas_token("ibm,get-system-parameter");
 	char *ptr, *key, *value, *end;
 	int call_status;
 	int page_order = IOMMU_PAGE_SHIFT_4K;
 
 	pr_debug(" -> fw_cmo_feature_init()\n");
-	spin_lock(&rtas_data_buf_lock);
-	memset(rtas_data_buf, 0, RTAS_DATA_BUF_SIZE);
-	call_status = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
-				NULL,
-				CMO_CHARACTERISTICS_TOKEN,
-				__pa(rtas_data_buf),
-				RTAS_DATA_BUF_SIZE);
 
-	if (call_status != 0) {
+	do {
+		spin_lock(&rtas_data_buf_lock);
+		call_status = rtas_call(token, 3, 1, NULL,
+					CMO_CHARACTERISTICS_TOKEN,
+					__pa(rtas_data_buf),
+					RTAS_DATA_BUF_SIZE);
+		if (call_status == 0)
+			break;
 		spin_unlock(&rtas_data_buf_lock);
+	} while (rtas_busy_delay(call_status));
+
+	if (call_status != 0) {
 		pr_debug("CMO not available\n");
 		pr_debug(" <- fw_cmo_feature_init()\n");
 		return;