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 <stable@vger.kernel.org>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 98593e0344c521c1d19fb57c2c64988386a90edf..27bb6d3877ed6cc64ea1fc5bde5c1094a6ab34b0 100644 (file)
--- 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;