Document special nature of setCS in comments

SPI.cpp

 	return true;
 }
 
+// setCS() is not intended for use from normal Arduino programs/sketches.
 uint8_t SPIClass::setCS(uint8_t pin)
 {
 	switch (pin) {
 	return true;
 }
 
+// setCS() is not intended for use from normal Arduino programs/sketches.
 uint8_t SPI1Class::setCS(uint8_t pin)
 {
 	switch (pin) {
 	return true;
 }
 
+// setCS() is not intended for use from normal Arduino programs/sketches.
 uint8_t SPI2Class::setCS(uint8_t pin)
 {
 	switch (pin) {
 	SPI_BR_SPPR(5) | SPI_BR_SPR(6)
 };
 
+// setCS() is not intended for use from normal Arduino programs/sketches.
 uint8_t SPIClass::setCS(uint8_t pin)
 {
 	switch (pin) {
 	SPI1_C1 = 0;
 }
 
+// setCS() is not intended for use from normal Arduino programs/sketches.
 uint8_t SPI1Class::setCS(uint8_t pin)
 {
 	switch (pin) {

SPI.h

 	// return true if both pin1 and pin2 have independent chip select capability
 	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2);
 	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	// setCS() is a special function, not intended for use from normal Arduino
+	// programs/sketches.  See the ILI3941_t3 library for an example.
 	static uint8_t setCS(uint8_t pin);
 
 private:
 	// return true if both pin1 and pin2 have independent chip select capability
 	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2);
 	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	// setCS() is a special function, not intended for use from normal Arduino
+	// programs/sketches.  See the ILI3941_t3 library for an example.
 	static uint8_t setCS(uint8_t pin);
 
 private:
 	// return true if both pin1 and pin2 have independent chip select capability
 	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2);
 	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	// setCS() is a special function, not intended for use from normal Arduino
+	// programs/sketches.  See the ILI3941_t3 library for an example.
 	static uint8_t setCS(uint8_t pin);
 
 private:
 	// return true if both pin1 and pin2 have independent chip select capability
 	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2) { return false; }
 	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	// setCS() is a special function, not intended for use from normal Arduino
+	// programs/sketches.  See the ILI3941_t3 library for an example.
 	static uint8_t setCS(uint8_t pin);
 
 private:
 	// return true if both pin1 and pin2 have independent chip select capability
 	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2) { return false; }
 	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	// setCS() is a special function, not intended for use from normal Arduino
+	// programs/sketches.  See the ILI3941_t3 library for an example.
 	static uint8_t setCS(uint8_t pin);
 
 private: