[Skiboot] [PATCH v8 2/4] occ: Fix Pstate ordering for P9

[Vaidyanathan Srinivasan]

From: Shilpasri G Bhat <shilpa.bhat at linux.vnet.ibm.com>

In P9 the pstate values are positive. They are continuous set of
unsigned integers [0 to +N] where Pmax is 0 and Pmin is N. The
linear ordering of pstates for P9 has changed compared to P8.
P8 has neagtive pstate values advertised as [0 to -N] where Pmax
is 0 and Pmin is -N. This patch adds helper routines to abstract
pstate comparison with pmax and adds sanity pstate limit checks.
This patch also fixes pstate arithmetic by using labs().

Suggested-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
Signed-off-by: Shilpasri G Bhat <shilpa.bhat at linux.vnet.ibm.com>
---
 hw/occ.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 98 insertions(+), 4 deletions(-)

diff --git a/hw/occ.c b/hw/occ.c
index 2720b7b..039b0fc 100644
--- a/hw/occ.c
+++ b/hw/occ.c
@@ -84,6 +84,50 @@ DEFINE_LOG_ENTRY(OPAL_RC_OCC_TIMEOUT, OPAL_PLATFORM_ERR_EVT, OPAL_OCC,
 		OPAL_CEC_HARDWARE, OPAL_UNRECOVERABLE_ERR_GENERAL,
 		OPAL_NA);
 
+/*
+ * POWER9 and newer platforms have pstate values which are unsigned
+ * positive values.  They are continuous set of unsigned integers
+ * [0 to +N] where Pmax is 0 and Pmin is N. The linear ordering of
+ * pstates for P9 has changed compared to P8.  Where P8 has negative
+ * pstate values advertised as [0 to -N] where Pmax is 0 and
+ * Pmin is -N.  The following routine helps to abstract pstate
+ * comparison with pmax and perform sanity checks on pstate limits.
+ */
+
+/**
+ * cmp_pstates: Compares the given two pstates and determines which
+ *              among them is associated with a higher pstate.
+ *
+ * @a, at b: The pstate ids of the pstates being compared.
+ *
+ * Returns: -1 : If pstate associated with @a is smaller than
+ *               the pstate associated with @b.
+ *	     0 : If pstates associated with @a and @b are equal.
+ *	     1 : If pstate associated with @a is greater than
+ *               the pstate associated with @b.
+ */
+static int (*cmp_pstates)(int a, int b);
+
+static int cmp_positive_pstates(int a, int b)
+{
+	if (a > b)
+		return -1;
+	else if (a < b)
+		return 1;
+
+	return 0;
+}
+
+static int cmp_negative_pstates(int a, int b)
+{
+	if (a < b)
+		return -1;
+	else if (a > b)
+		return 1;
+
+	return 0;
+}
+
 /* Check each chip's HOMER/Sapphire area for PState valid bit */
 static bool wait_for_all_occ_init(void)
 {
@@ -214,15 +258,38 @@ static bool add_cpu_pstate_properties(s8 *pstate_nom)
 		return false;
 	}
 
+	/*
+	 * Workload-Optimized-Frequency(WOF) or Ultra-Turbo is supported
+	 * from version 2 onwards. If WOF is disabled then, the max
+	 * ultra_turbo pstate will be equal to max turbo pstate.
+	 */
 	if (occ_data->version > 1 &&
-	    occ_data->pstate_ultra_turbo > occ_data->pstate_turbo)
+	    cmp_pstates(occ_data->pstate_ultra_turbo,
+			occ_data->pstate_turbo) > 0)
 		ultra_turbo_en = true;
 	else
 		ultra_turbo_en = false;
 
 	pmax = ultra_turbo_en ? occ_data->pstate_ultra_turbo :
 				occ_data->pstate_turbo;
-	nr_pstates = pmax - occ_data->pstate_min + 1;
+
+	/* Sanity check for pstate limits */
+	if (cmp_pstates(occ_data->pstate_min, pmax) > 0) {
+		/**
+		 * @fwts-label OCCInvalidPStateLimits
+		 * @fwts-advice The min pstate is greater than the
+		 * max pstate, this could be due to corrupted/invalid
+		 * data in OCC-OPAL shared memory region. So OPAL has
+		 * not added pstates to device tree. This means that
+		 * CPU Frequency management will not be functional in
+		 * the host.
+		 */
+		prlog(PR_ERR, "OCC: Invalid Pstate Limits. Pmin(%d) > Pmax (%d)\n",
+		      occ_data->pstate_min, pmax);
+		return false;
+	}
+
+	nr_pstates = labs(pmax - occ_data->pstate_min) + 1;
 	prlog(PR_DEBUG, "OCC: Min %d Nom %d Max %d Nr States %d\n", 
 	      occ_data->pstate_min, occ_data->pstate_nom,
 	      pmax, nr_pstates);
@@ -319,15 +386,31 @@ static bool add_cpu_pstate_properties(s8 *pstate_nom)
 			dt_core_max[i] = occ_data->core_max[i];
 	}
 
+	/*
+	 * OCC provides pstate table entries in continuous descending order.
+	 * Parse the pstate table to skip pstate_ids that are greater
+	 * than Pmax. If a pstate_id is equal to Pmin then add it to
+	 * the list and break from the loop as this is the last valid
+	 * element in the pstate table.
+	 */
 	for (i = 0, j = 0; i < MAX_PSTATES && j < nr_pstates; i++) {
-		if (occ_data->pstates[i].id > pmax ||
-		    occ_data->pstates[i].id < occ_data->pstate_min)
+		if (cmp_pstates(occ_data->pstates[i].id, pmax) > 0)
 			continue;
+
 		dt_id[j] = occ_data->pstates[i].id;
 		dt_freq[j] = occ_data->pstates[i].freq_khz / 1000;
 		dt_vdd[j] = occ_data->pstates[i].vdd;
 		dt_vcs[j] = occ_data->pstates[i].vcs;
 		j++;
+
+		if (occ_data->pstates[i].id == occ_data->pstate_min)
+			break;
+	}
+
+	if (j != nr_pstates) {
+		prerror("OCC: Expected pstates(%d) is not equal to parsed pstates(%d)\n",
+			nr_pstates, j);
+		goto out_free_vcs;
 	}
 
 	/* Add the device-tree entries */
@@ -533,6 +616,17 @@ void occ_pstates_init(void)
 	if (occ_pstates_initialized)
 		return;
 
+	switch (proc_gen) {
+	case proc_gen_p8:
+		cmp_pstates = cmp_negative_pstates;
+		break;
+	case proc_gen_p9:
+		cmp_pstates = cmp_positive_pstates;
+		break;
+	default:
+		return;
+	}
+
 	chip = next_chip(NULL);
 	if (!chip->homer_base) {
 		log_simple_error(&e_info(OPAL_RC_OCC_PSTATE_INIT),
-- 
2.9.4