hwmon: (fam15h_power) Increase output resolution

On high CPU load the accumulating values in the running_avg_cap
register are very low (below 10), so averaging them too early leads
to unnecessary poor output resolution. Since we pretend to output
micro-Watt we better keep all the bits we have as long as possible.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
(cherry picked from commit 941a956b0e387b21f385f486c34ef67576775cfc)

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
index 9a4c3ab..e8e18ca 100644 (file)
--- a/drivers/hwmon/fam15h_power.c
+++ b/drivers/hwmon/fam15h_power.c
@@ -61,14 +61,14 @@ static ssize_t show_power(struct device *dev,
                                  REG_TDP_RUNNING_AVERAGE, &val);
        running_avg_capture = (val >> 4) & 0x3fffff;
        running_avg_capture = sign_extend32(running_avg_capture, 21);
-       running_avg_range = val & 0xf;
+       running_avg_range = (val & 0xf) + 1;
 
        pci_bus_read_config_dword(f4->bus, PCI_DEVFN(PCI_SLOT(f4->devfn), 5),
                                  REG_TDP_LIMIT3, &val);
 
        tdp_limit = val >> 16;
-       curr_pwr_watts = tdp_limit + data->base_tdp -
-               (s32)(running_avg_capture >> (running_avg_range + 1));
+       curr_pwr_watts = (tdp_limit + data->base_tdp) << running_avg_range;
+       curr_pwr_watts -= running_avg_capture;
        curr_pwr_watts *= data->tdp_to_watts;
 
        /*
@@ -78,7 +78,7 @@ static ssize_t show_power(struct device *dev,
         * scaling factor 1/(2^16).  For conversion we use
         * (10^6)/(2^16) = 15625/(2^10)
         */
-       curr_pwr_watts = (curr_pwr_watts * 15625) >> 10;
+       curr_pwr_watts = (curr_pwr_watts * 15625) >> (10 + running_avg_range);
        return sprintf(buf, "%u\n", (unsigned int) curr_pwr_watts);
 }
 static DEVICE_ATTR(power1_input, S_IRUGO, show_power, NULL);