thermal: k3_j72xx_bandgap: Add the bandgap driver support

Add VTM thermal support. In the Voltage Thermal Management
Module(VTM), K3 J72XX supplies a voltage reference and a temperature
sensor feature that are gathered in the band gap voltage and
temperature sensor (VBGAPTS) module. The band gap provides current and
voltage reference for its internal circuits and other analog IP
blocks. The analog-to-digital converter (ADC) produces an output value
that is proportional to the silicon temperature.

Currently reading temperatures only is supported.  There are no
active/passive cooling agent supported.

J721e SoCs have errata i2128: https://www.ti.com/lit/pdf/sprz455

The VTM Temperature Monitors (TEMPSENSORs) are trimmed during production,
with the resulting values stored in software-readable registers. Software
should use these  register values when translating the Temperature
Monitor output codes to temperature values.

It has an involved workaround. Software needs to read the error codes for
-40C, 30C, 125C from the efuse for each device & derive a new look up table
for adc to temperature conversion. Involved calculating slopes & constants
using 3 different straight line equations with adc refernce codes as the
y-axis & error codes in the x-axis.

-40C to 30C
30C to 125C
125C to 150C

With the above 2 line equations we derive the full look-up table to
workaround the errata i2128 for j721e SoC.

Tested temperature reading on J721e SoC & J7200 SoC.

[[email protected]: Generate look-up tables run-time]

Signed-off-by: Daniel Lezcano <[email protected]>
Signed-off-by: Keerthy <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Daniel Lezcano <[email protected]>

Author: Keerthyj

drivers/thermal/Makefile

@@ -28,7 +28,7 @@ thermal_sys-$(CONFIG_CPU_IDLE_THERMAL)	+= cpuidle_cooling.o
 # devfreq cooling
 thermal_sys-$(CONFIG_DEVFREQ_THERMAL) += devfreq_cooling.o
 
-obj-$(CONFIG_K3_THERMAL)	+= k3_bandgap.o
+obj-$(CONFIG_K3_THERMAL)	+= k3_bandgap.o k3_j72xx_bandgap.o
 # platform thermal drivers
 obj-y				+= broadcom/
 obj-$(CONFIG_THERMAL_MMIO)		+= thermal_mmio.o