Commit d022a65e authored Oct 13, 2014 by Dirk Brandewie Committed by Rafael J. Wysocki Oct 23, 2014

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>

parent b27580b0

drivers/cpufreq/intel_pstate.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -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;