iio: adc: vf610: Determine sampling frequencies by using minimum sample time
The driver currently does not take into account the minimum sample time
as per the Figure 6-8 Chapter 9.1.1 12-bit ADC electrical characteristics.
We set a static amount of cycles instead of considering the sample time
as a given value, which depends on hardware characteristics.
Determine sampling frequencies by first reading the device tree property
node and then calculating the required Long Sample Time Adder (LSTAdder)
value, based on the ADC clock frequency and sample time value obtained
from the device tree. This LSTAdder value is then used for calculating
the sampling frequencies possible.
In case the sample time property is not specified through the device
tree, a safe default value of 1000ns is assumed.
Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Acked-by: Stefan Agner <stefan@agner.ch>
Acked-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
index 3eb40e2..1aad051 100644
--- a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
+++ b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
@@ -17,6 +17,11 @@
- Frequency in normal mode (ADLPC=0, ADHSC=0)
- Frequency in high-speed mode (ADLPC=0, ADHSC=1)
- Frequency in low-power mode (ADLPC=1, ADHSC=0)
+- min-sample-time: Minimum sampling time in nanoseconds. This value has
+ to be chosen according to the conversion mode and the connected analog
+ source resistance (R_as) and capacitance (C_as). Refer the datasheet's
+ operating requirements. A safe default across a wide range of R_as and
+ C_as as well as conversion modes is 1000ns.
Example:
adc0: adc@4003b000 {