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Date: Thu, 7 Dec 2017 22:25:15 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
huntbag@...ux.vnet.ibm.com, akshay.adiga@...ux.vnet.ibm.com,
Michael Ellerman <mpe@...erman.id.au>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Linux PM <linux-pm@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
Stable <stable@...r.kernel.org>
Subject: Re: [v2 PATCH] cpufreq: powernv: Correctly parse the sign of pstates
on POWER8 vs POWER9
On Thu, Dec 7, 2017 at 6:59 AM, Gautham R. Shenoy
<ego@...ux.vnet.ibm.com> wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
>
> On POWERNV platform, Pstates are 8-bit values. On POWER8 they are
> negatively numbered while on POWER9 they are positively
> numbered. Thus, on POWER9, the maximum number of pstates could be as
> high as 256.
>
> The current code interprets pstates as a signed 8-bit value. This
> causes a problem on POWER9 platforms which have more than 128 pstates.
> On such systems, on a CPU that is in a lower pstate whose number is
> greater than 128, querying the current pstate returns a "pstate X is
> out of bound" error message and the current pstate is reported as the
> nominal pstate.
>
> This patch fixes the aforementioned issue by correctly differentiating
> the sign whenever a pstate value read, depending on whether the
> pstates are positively numbered or negatively numbered.
>
> Fixes: commit 09ca4c9b5958 ("cpufreq: powernv: Replacing pstate_id with frequency table index")
> Cc: <stable@...r.kernel.org> #v4.8
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> Tested-and-reviewed-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
I'm going to apply this, or please let me know if you want to route it
differently.
> ---
> drivers/cpufreq/powernv-cpufreq.c | 43 ++++++++++++++++++++++++++++++---------
> 1 file changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index b6d7c4c..bb7586e 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -41,11 +41,14 @@
> #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 EXTRACT_BYTE(x, shift) (((x) >> shift) & 0xFF)
> +#define MAX_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 GET_PMSR_MAX(x) EXTRACT_BYTE(x, MAX_SHIFT)
> +#define GET_LPSTATE(x) EXTRACT_BYTE(x, LPSTATE_SHIFT)
> +#define GET_GPSTATE(x) EXTRACT_BYTE(x, GPSTATE_SHIFT)
> +
>
> #define MAX_RAMP_DOWN_TIME 5120
> /*
> @@ -64,6 +67,12 @@
>
> /* Interval after which the timer is queued to bring down global pstate */
> #define GPSTATE_TIMER_INTERVAL 2000
> +/*
> + * On POWER8 the pstates are negatively numbered. On POWER9, they are
> + * positively numbered. Use this flag to track whether we have
> + * positive or negative numbered pstates.
> + */
> +static bool pos_pstates;
>
> /**
> * struct global_pstate_info - Per policy data structure to maintain history of
> @@ -164,7 +173,7 @@ static inline unsigned int pstate_to_idx(int pstate)
> int min = powernv_freqs[powernv_pstate_info.min].driver_data;
> int max = powernv_freqs[powernv_pstate_info.max].driver_data;
>
> - if (min > 0) {
> + if (pos_pstates) {
> if (unlikely((pstate < max) || (pstate > min))) {
> pr_warn_once("pstate %d is out of bound\n", pstate);
> return powernv_pstate_info.nominal;
> @@ -301,6 +310,9 @@ static int init_powernv_pstates(void)
> }
> }
>
> + if ((int)pstate_min > 0)
> + pos_pstates = true;
> +
> /* End of list marker entry */
> powernv_freqs[i].frequency = CPUFREQ_TABLE_END;
> return 0;
> @@ -438,7 +450,6 @@ 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);
> @@ -447,8 +458,11 @@ static void powernv_read_cpu_freq(void *arg)
> * 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;
> + if (pos_pstates)
> + freq_data->pstate_id = (u8)GET_LPSTATE(pmspr_val);
> + else
> + freq_data->pstate_id = (s8)GET_LPSTATE(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 +536,10 @@ static void powernv_cpufreq_throttle_check(void *data)
> chip = this_cpu_read(chip_info);
>
> /* Check for Pmax Capping */
> - pmsr_pmax = (s8)PMSR_MAX(pmsr);
> + if (pos_pstates)
> + pmsr_pmax = (u8)GET_PMSR_MAX(pmsr);
> + else
> + pmsr_pmax = (s8)GET_PMSR_MAX(pmsr);
> pmsr_pmax_idx = pstate_to_idx(pmsr_pmax);
> if (pmsr_pmax_idx != powernv_pstate_info.max) {
> if (chip->throttled)
> @@ -645,8 +662,14 @@ 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);
> + if (pos_pstates) {
> + freq_data.gpstate_id = (u8)GET_GPSTATE(val);
> + freq_data.pstate_id = (u8)GET_LPSTATE(val);
> + } else {
> + freq_data.gpstate_id = (s8)GET_GPSTATE(val);
> + freq_data.pstate_id = (s8)GET_LPSTATE(val);
> + }
> +
> if (freq_data.gpstate_id == freq_data.pstate_id) {
> reset_gpstates(policy);
> spin_unlock(&gpstates->gpstate_lock);
> --
> 1.8.3.1
>
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