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Subject[v3 PATCH 1/3] powernv-cpufreq: Add helper to extract pstate from PMSR
Date
From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

On POWERNV platform, the fields for pstates in the Power Management
Status Register (PMSR) and the Power Management Control Register
(PMCR) are 8-bits wide. On POWER8 the pstates are negatively numbered
while on POWER9 they are positively numbered.

The device-tree exports pstates as 32-bit entries. The device-tree
implementation sign-extends the 8-bit pstate values to obtain the
corresponding 32-bit entry.

Eg: On POWER8, a pstate value 0x82 [-126] is represented in the
device-tree as 0xfffffff82 while on POWER9, the same value 0x82 [130]
is represented in the device-tree as 0x00000082.

The powernv-cpufreq driver implementation represents pstates using the
integer type. In multiple places in the driver, the code interprets
the pstates extracted from the PMSR as a signed byte and assigns it to
a integer variable to get the sign-extention.

On POWER9 platforms which have greater than 128 pstates, this results
in the driver performing incorrect sign-extention, and thereby
treating a legitimate pstate (say 130) as an invalid pstates (since it
is interpreted as -126).

This patch fixes the issue by implementing a helper function to
extract Pstates from PMSR register, and correctly sign-extend it to be
consistent with the values provided by the device-tree.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
drivers/cpufreq/powernv-cpufreq.c | 37 +++++++++++++++++++++++--------------
1 file changed, 23 insertions(+), 14 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index b6d7c4c..f46b60f 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -41,11 +41,9 @@
#define POWERNV_MAX_PSTATES 256
#define PMSR_PSAFE_ENABLE (1UL << 30)
#define PMSR_SPR_EM_DISABLE (1UL << 31)
-#define PMSR_MAX(x) ((x >> 32) & 0xFF)
+#define MAX_PSTATE_SHIFT 32
#define LPSTATE_SHIFT 48
#define GPSTATE_SHIFT 56
-#define GET_LPSTATE(x) (((x) >> LPSTATE_SHIFT) & 0xFF)
-#define GET_GPSTATE(x) (((x) >> GPSTATE_SHIFT) & 0xFF)

#define MAX_RAMP_DOWN_TIME 5120
/*
@@ -94,6 +92,7 @@ struct global_pstate_info {
};

static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
+u32 pstate_sign_prefix;
static bool rebooting, throttled, occ_reset;

static const char * const throttle_reason[] = {
@@ -148,6 +147,20 @@ enum throttle_reason_type {
bool wof_enabled;
} powernv_pstate_info;

+static inline int extract_pstate(u64 pmsr_val, unsigned int shift)
+{
+ int ret = ((pmsr_val >> shift) & 0xFF);
+
+ if (!ret)
+ return ret;
+
+ return (pstate_sign_prefix | ret);
+}
+
+#define extract_local_pstate(x) extract_pstate(x, LPSTATE_SHIFT)
+#define extract_global_pstate(x) extract_pstate(x, GPSTATE_SHIFT)
+#define extract_max_pstate(x) extract_pstate(x, MAX_PSTATE_SHIFT)
+
/* Use following macros for conversions between pstate_id and index */
static inline int idx_to_pstate(unsigned int i)
{
@@ -278,6 +291,9 @@ static int init_powernv_pstates(void)

powernv_pstate_info.nr_pstates = nr_pstates;
pr_debug("NR PStates %d\n", nr_pstates);
+
+ pstate_sign_prefix = pstate_min & ~0xFF;
+
for (i = 0; i < nr_pstates; i++) {
u32 id = be32_to_cpu(pstate_ids[i]);
u32 freq = be32_to_cpu(pstate_freqs[i]);
@@ -438,17 +454,10 @@ struct powernv_smp_call_data {
static void powernv_read_cpu_freq(void *arg)
{
unsigned long pmspr_val;
- s8 local_pstate_id;
struct powernv_smp_call_data *freq_data = arg;

pmspr_val = get_pmspr(SPRN_PMSR);
-
- /*
- * The local pstate id corresponds bits 48..55 in the PMSR.
- * Note: Watch out for the sign!
- */
- local_pstate_id = (pmspr_val >> 48) & 0xFF;
- freq_data->pstate_id = local_pstate_id;
+ freq_data->pstate_id = extract_local_pstate(pmspr_val);
freq_data->freq = pstate_id_to_freq(freq_data->pstate_id);

pr_debug("cpu %d pmsr %016lX pstate_id %d frequency %d kHz\n",
@@ -522,7 +531,7 @@ static void powernv_cpufreq_throttle_check(void *data)
chip = this_cpu_read(chip_info);

/* Check for Pmax Capping */
- pmsr_pmax = (s8)PMSR_MAX(pmsr);
+ pmsr_pmax = extract_max_pstate(pmsr);
pmsr_pmax_idx = pstate_to_idx(pmsr_pmax);
if (pmsr_pmax_idx != powernv_pstate_info.max) {
if (chip->throttled)
@@ -645,8 +654,8 @@ void gpstate_timer_handler(struct timer_list *t)
* value. Hence, read from PMCR to get correct data.
*/
val = get_pmspr(SPRN_PMCR);
- freq_data.gpstate_id = (s8)GET_GPSTATE(val);
- freq_data.pstate_id = (s8)GET_LPSTATE(val);
+ freq_data.gpstate_id = extract_global_pstate(val);
+ freq_data.pstate_id = extract_local_pstate(val);
if (freq_data.gpstate_id == freq_data.pstate_id) {
reset_gpstates(policy);
spin_unlock(&gpstates->gpstate_lock);
--
1.9.4
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