linux-kernel - [PATCH 3.13 094/162] intel_pstate: Correct BYT VID values.

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Message-Id: <1415313426-9622-95-git-send-email-kamal@canonical.com>
Date:	Thu,  6 Nov 2014 14:35:58 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Dirk Brandewie <dirk.j.brandewie@...el.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13 094/162] intel_pstate: Correct BYT VID values.

3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dirk Brandewie <dirk.j.brandewie@...el.com>

commit d022a65ed2473fac4a600e3424503dc571160a3e upstream.

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)

Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 2cb7028..4e8949d 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -54,6 +54,17 @@ static inline int32_t div_fp(int32_t x, int32_t y)
 	return div_s64((int64_t)x << FRAC_BITS, (int64_t)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;
@@ -428,7 +439,7 @@ 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;
-- 
1.9.1

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