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From:   "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@gmail.com>,
        Anton Blanchard <anton@ozlabs.org>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michael Neuling <mikey@neuling.org>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc:     linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org,
        "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Subject: [PATCH v3 2/3] cpuidle-pseries: Add function to parse extended CEDE records
Date:   Thu, 30 Jul 2020 11:02:56 +0530
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From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

Currently we use CEDE with latency-hint 0 as the only other idle state
on a dedicated LPAR apart from the polling "snooze" state.

The platform might support additional extended CEDE idle states, which
can be discovered through the "ibm,get-system-parameter" rtas-call
made with CEDE_LATENCY_TOKEN.

This patch adds a function to obtain information about the extended
CEDE idle states from the platform and parse the contents to populate
an array of extended CEDE states. These idle states thus discovered
will be added to the cpuidle framework in the next patch.

dmesg on a POWER8 and POWER9 LPAR, demonstrating the output of parsing
the extended CEDE latency parameters are as follows

POWER8
[   10.093279] xcede : xcede_record_size = 10
[   10.093285] xcede : Record 0 : hint = 1, latency = 0x3c00 tb ticks, Wake-on-irq = 1
[   10.093291] xcede : Record 1 : hint = 2, latency = 0x4e2000 tb ticks, Wake-on-irq = 0
[   10.093297] cpuidle : Skipping the 2 Extended CEDE idle states

POWER9
[    5.913180] xcede : xcede_record_size = 10
[    5.913183] xcede : Record 0 : hint = 1, latency = 0x400 tb ticks, Wake-on-irq = 1
[    5.913188] xcede : Record 1 : hint = 2, latency = 0x3e8000 tb ticks, Wake-on-irq = 0
[    5.913193] cpuidle : Skipping the 2 Extended CEDE idle states

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
v2-->v3 : Cleaned up parse_cede_parameters(). Silenced some sparse warnings.
drivers/cpuidle/cpuidle-pseries.c | 142 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index f5865a2..f528da7 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -21,6 +21,7 @@
 #include <asm/runlatch.h>
 #include <asm/idle.h>
 #include <asm/plpar_wrappers.h>
+#include <asm/rtas.h>
 
 static struct cpuidle_driver pseries_idle_driver = {
 	.name             = "pseries_idle",
@@ -87,6 +88,137 @@ static void check_and_cede_processor(void)
 }
 
 #define NR_DEDICATED_STATES	2 /* snooze, CEDE */
+/*
+ * XCEDE : Extended CEDE states discovered through the
+ *         "ibm,get-systems-parameter" rtas-call with the token
+ *         CEDE_LATENCY_TOKEN
+ */
+#define MAX_XCEDE_STATES		4
+#define	XCEDE_LATENCY_RECORD_SIZE	10
+#define XCEDE_LATENCY_PARAM_MAX_LENGTH	(2 + 2 + \
+					(MAX_XCEDE_STATES * XCEDE_LATENCY_RECORD_SIZE))
+
+/*
+ * Section 7.3.16 System Parameters Option of PAPR version 2.8.1 has a
+ * table with all the parameters to ibm,get-system-parameters.
+ * CEDE_LATENCY_TOKEN corresponds to the token value for Cede Latency
+ * Settings Information.
+ */
+#define CEDE_LATENCY_TOKEN		45
+
+/*
+ * If the platform supports the cede latency settings
+ * information system parameter it must provide the following
+ * information in the NULL terminated parameter string:
+ *
+ * a. The first byte is the length “N” of each cede
+ *    latency setting record minus one (zero indicates a length
+ *    of 1 byte).
+ *
+ * b. For each supported cede latency setting a cede latency
+ *    setting record consisting of the first “N” bytes as per
+ *    the following table.
+ *
+ *	-----------------------------
+ *	| Field           | Field  |
+ *	| Name            | Length |
+ *	-----------------------------
+ *	| Cede Latency    | 1 Byte |
+ *	| Specifier Value |        |
+ *	-----------------------------
+ *	| Maximum wakeup  |        |
+ *	| latency in      | 8 Bytes|
+ *	| tb-ticks        |        |
+ *	-----------------------------
+ *	| Responsive to   |        |
+ *	| external        | 1 Byte |
+ *	| interrupts      |        |
+ *	-----------------------------
+ *
+ * This version has cede latency record size = 10.
+ *
+ * The structure xcede_latency_payload represents a) and b) with
+ * xcede_latency_record representing the table in b).
+ *
+ * xcede_latency_parameter is what gets returned by
+ * ibm,get-systems-parameter rtas-call when made with
+ * CEDE_LATENCY_TOKEN.
+ *
+ * These structures are only used to represent the data sent obtained
+ * by the rtas-call. The data is in Big-Endian.
+ */
+struct xcede_latency_record {
+	u8	hint;
+	__be64	latency_ticks;
+	u8	wake_on_irqs;
+} __packed;
+
+struct xcede_latency_payload {
+	u8     record_size;
+	struct xcede_latency_record records[MAX_XCEDE_STATES];
+} __packed;
+
+struct xcede_latency_parameter {
+	__be16  payload_size;
+	struct xcede_latency_payload payload;
+	u8 null_char;
+} __packed;
+
+static unsigned int nr_xcede_records;
+static struct xcede_latency_parameter xcede_latency_parameter __initdata;
+
+static int __init parse_cede_parameters(void)
+{
+	int ret, i;
+	u16 payload_size;
+	u8 xcede_record_size;
+	u32 total_xcede_records_size;
+	struct xcede_latency_payload *payload;
+
+	memset(&xcede_latency_parameter, 0, sizeof(xcede_latency_parameter));
+
+	ret = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
+			NULL, CEDE_LATENCY_TOKEN, __pa(&xcede_latency_parameter),
+			sizeof(xcede_latency_parameter));
+
+	if (ret) {
+		pr_err("xcede: Error parsing CEDE_LATENCY_TOKEN\n");
+		return ret;
+	}
+
+	payload_size = be16_to_cpu(xcede_latency_parameter.payload_size);
+	payload = &xcede_latency_parameter.payload;
+
+	xcede_record_size = payload->record_size + 1;
+
+	if (xcede_record_size != XCEDE_LATENCY_RECORD_SIZE) {
+		pr_err("xcede : Expected record-size %d. Observed size %d.\n",
+		       XCEDE_LATENCY_RECORD_SIZE, xcede_record_size);
+		return -EINVAL;
+	}
+
+	pr_info("xcede : xcede_record_size = %d\n", xcede_record_size);
+
+	/*
+	 * Since the payload_length includes the last NULL byte and
+	 * the xcede_record_size, the remaining bytes correspond to
+	 * array of all cede_latency settings.
+	 */
+	total_xcede_records_size = payload_size - 2;
+	nr_xcede_records = total_xcede_records_size / xcede_record_size;
+
+	for (i = 0; i < nr_xcede_records; i++) {
+		struct xcede_latency_record *record = &payload->records[i];
+		u8 hint = record->hint;
+		u8 wake_on_irqs = record->wake_on_irqs;
+		u64 latency_ticks = be64_to_cpu(record->latency_ticks);
+
+		pr_info("xcede : Record %d : hint = %u, latency = 0x%llx tb ticks, Wake-on-irq = %u\n",
+			i, hint, latency_ticks, wake_on_irqs);
+	}
+
+	return 0;
+}
 
 u8 cede_latency_hint[NR_DEDICATED_STATES];
 static int dedicated_cede_loop(struct cpuidle_device *dev,
@@ -218,6 +350,15 @@ static int pseries_cpuidle_driver_init(void)
 	return 0;
 }
 
+static void __init parse_xcede_idle_states(void)
+{
+	if (parse_cede_parameters())
+		return;
+
+	pr_info("cpuidle : Skipping the %d Extended CEDE idle states\n",
+		nr_xcede_records);
+}
+
 /*
  * pseries_idle_probe()
  * Choose state table for shared versus dedicated partition
@@ -239,6 +380,7 @@ static int pseries_idle_probe(void)
 			cpuidle_state_table = shared_states;
 			max_idle_state = ARRAY_SIZE(shared_states);
 		} else {
+			parse_xcede_idle_states();
 			cpuidle_state_table = dedicated_states;
 			max_idle_state = NR_DEDICATED_STATES;
 		}
-- 
1.9.4