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[PATCH 3.16 031/114] Input: pmic8xxx-pwrkey - fix algorithm for converting trigger delay

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3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Stephen Boyd <sboyd@codeaurora.org>

commit eda5ecc0a6b865561997e177c393f0b0136fe3b7 upstream.

The trigger delay algorithm that converts from microseconds to
the register value looks incorrect. According to most of the PMIC
documentation, the equation is

	delay (Seconds) = (1 / 1024) * 2 ^ (x + 4)

except for one case where the documentation looks to have a
formatting issue and the equation looks like

	delay (Seconds) = (1 / 1024) * 2 x + 4

Most likely this driver was written with the improper
documentation to begin with. According to the downstream sources
the valid delays are from 2 seconds to 1/64 second, and the
latter equation just doesn't make sense for that. Let's fix the
algorithm and the range check to match the documentation and the
downstream sources.

Reported-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Fixes: 92d57a73e410 ("input: Add support for Qualcomm PMIC8XXX power key")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/input/misc/pmic8xxx-pwrkey.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/input/misc/pmic8xxx-pwrkey.c
+++ b/drivers/input/misc/pmic8xxx-pwrkey.c
@@ -94,7 +94,8 @@ static int pmic8xxx_pwrkey_probe(struct
 	if (of_property_read_u32(pdev->dev.of_node, "debounce", &kpd_delay))
 		kpd_delay = 15625;
 
-	if (kpd_delay > 62500 || kpd_delay == 0) {
+	/* Valid range of pwr key trigger delay is 1/64 sec to 2 seconds. */
+	if (kpd_delay > USEC_PER_SEC * 2 || kpd_delay < USEC_PER_SEC / 64) {
 		dev_err(&pdev->dev, "invalid power key trigger delay\n");
 		return -EINVAL;
 	}
@@ -124,8 +125,8 @@ static int pmic8xxx_pwrkey_probe(struct
 	pwr->name = "pmic8xxx_pwrkey";
 	pwr->phys = "pmic8xxx_pwrkey/input0";
 
-	delay = (kpd_delay << 10) / USEC_PER_SEC;
-	delay = 1 + ilog2(delay);
+	delay = (kpd_delay << 6) / USEC_PER_SEC;
+	delay = ilog2(delay);
 
 	err = regmap_read(regmap, PON_CNTL_1, &pon_cntl);
 	if (err < 0) {

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[PATCH 3.16 031/114] Input: pmic8xxx-pwrkey - fix algorithm for  converting trigger delay Ben Hutchings <ben@decadent.org.uk> - 2016-06-13 20:40 +0200

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