From d022a65ed2473fac4a600e3424503dc571160a3e Mon Sep 17 00:00:00 2001 From: Dirk Brandewie Date: Mon, 13 Oct 2014 08:37:44 -0700 Subject: intel_pstate: Correct BYT VID values. Using a VID value that is not high enough for the requested P state can cause machine checks. Add a ceiling function to ensure calulated VIDs with fractional values are set to the next highest integer VID value. The algorythm for calculating the non-trubo VID from the BIOS writers guide is: vid_ratio = (vid_max - vid_min) / (max_pstate - min_pstate) vid = ceiling(vid_min + (req_pstate - min_pstate) * vid_ratio) Cc: All applicable Signed-off-by: Dirk Brandewie Signed-off-by: Rafael J. Wysocki --- drivers/cpufreq/intel_pstate.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 98593e0344c5..27bb6d3877ed 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -52,6 +52,17 @@ static inline int32_t div_fp(int32_t x, int32_t y) return div_s64((int64_t)x << FRAC_BITS, y); } +static inline int ceiling_fp(int32_t x) +{ + int mask, ret; + + ret = fp_toint(x); + mask = (1 << FRAC_BITS) - 1; + if (x & mask) + ret += 1; + return ret; +} + struct sample { int32_t core_pct_busy; u64 aperf; @@ -425,7 +436,7 @@ static void byt_set_pstate(struct cpudata *cpudata, int pstate) cpudata->vid.ratio); vid_fp = clamp_t(int32_t, vid_fp, cpudata->vid.min, cpudata->vid.max); - vid = fp_toint(vid_fp); + vid = ceiling_fp(vid_fp); if (pstate > cpudata->pstate.max_pstate) vid = cpudata->vid.turbo; -- cgit v1.2.3-59-g8ed1b