thermal: generic-adc: make lookup table optional [Linux 5.2]

thermal: generic-adc: make lookup table optional [Linux 5.2]

This Linux kernel change "thermal: generic-adc: make lookup table optional" is included in the Linux 5.2 release. This change is authored by Jean-Francois Dagenais <jeff.dagenais [at] gmail.com> on Thu Apr 18 12:37:32 2019 -0400. The commit for this change in Linux stable tree is d36e2fa (patch).

thermal: generic-adc: make lookup table optional

Certain ADC channels, such as the xilinx-ams temperature channels, give
milliCelcius already when read with iio_read_channel_processed.

Rather than having to provide a 1:1 dummy lookup table, simply allow to
bypass the mechanism.

Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

There are 9 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/thermal/thermal-generic-adc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
index e22fc60..deb244f 100644
--- a/drivers/thermal/thermal-generic-adc.c
+++ b/drivers/thermal/thermal-generic-adc.c
@@ -29,6 +29,9 @@ static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
    int temp, temp_hi, temp_lo, adc_hi, adc_lo;
    int i;

+   if (!gti->lookup_table)
+       return val;
+
    for (i = 0; i < gti->nlookup_table; i++) {
        if (val >= gti->lookup_table[2 * i + 1])
            break;
@@ -81,9 +84,9 @@ static int gadc_thermal_read_linear_lookup_table(struct device *dev,

    ntable = of_property_count_elems_of_size(np, "temperature-lookup-table",
                         sizeof(u32));
-   if (ntable < 0) {
-       dev_err(dev, "Lookup table is not provided\n");
-       return ntable;
+   if (ntable <= 0) {
+       dev_notice(dev, "no lookup table, assuming DAC channel returns milliCelcius\n");
+       return 0;
    }

    if (ntable % 2) {

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