Troubleshooting: Add FAQ about GPIO numbering & available I²C interfaces

Signed-off-by: Stefan Wahren <stefan.wahren@chargebyte.com>

Author: lategoodbye

docs/source/troubleshooting.rst

@@ -49,6 +49,21 @@ we recommend the usage of chardev GPIO and libgpiod. The modification of the bia
 settings via libgpiod is not yet implemented, so it needs to be done via device tree.
 
 
+My application depends on libgpiod but requires GPIO numbers, how can I figure them out?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+For such legacy applications which rely on GPIO numbers, you can use the following:
+
+.. code-block:: console
+
+   root@chargesom:/# cat /sys/kernel/debug/gpio
+   gpiochip0: GPIOs 512-541, parent: platform/43810000.gpio, 43810000.gpio:
+   gpio-512 (SPI_PLC_nCS0        |spi1 CS0            ) out hi ACTIVE LOW
+   ...
+
+The GPIO number is in the first column ( gpio-XXX ).
+
+
 What is the difference between CHSTOP_IN and SAFETY_ESTOPx?
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -85,6 +100,20 @@ counting from zero (ttyLP0 = UART1, ...).
    4: uart:FSL_LPUART mmio:0x42590010 irq:20 tx:0 rx:0 CTS|DSR|CD
 
 
+How can I list the available I²C interfaces?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+All I²C interfaces are available via I²C device driver. Please keep in mind that
+Linux starts counting from zero (i2c-0 = I2C1, ...).
+
+.. code-block:: console
+
+   root@chargesom:/# i2cdetect -l
+   i2c-0   i2c             44340000.i2c                            I2C adapter
+   i2c-1   i2c             44350000.i2c                            I2C adapter
+   i2c-2   i2c             42530000.i2c                            I2C adapter
+
+
 How can I print the current pin/pad control settings (e.g. bias, drive strength)?
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^