Document return values of bcm_host_get_peripheral_* functions for…cl…

…arity.

Signed-off-by: Daniel Indictor <daniel.indictor@gmail.com>

host_applications/linux/libs/bcm_host/include/bcm_host.h

@@ -43,8 +43,19 @@ int32_t graphics_get_display_size( const uint16_t display_number,
                                                     uint32_t *width,
                                                     uint32_t *height);
 
+/* These functions refer to the peripherals that all Pi's share,
+ * which start 0x0200_0000 bytes higher than the "main peripheral"
+ * physical addresses from the BCM2xxx datasheets. For example,
+ * if you want the physical address of the GPIO's base address,
+ * you should add 0x0020_0000 to the value this function returns,
+ * since the GPIO base address is 0x0220_0000 bytes higher than the
+ * base address of the main peripherals.
+ * Source:
+ * https://github.com/raspberrypi/linux/blob/a90998a3e549911234f9f707050858b98b71360f/arch/arm/boot/dts/bcm2711.dtsi#L34
+ */
 unsigned bcm_host_get_peripheral_address(void);
 unsigned bcm_host_get_peripheral_size(void);
+
 unsigned bcm_host_get_sdram_address(void);
 
 #include "interface/vmcs_host/vc_dispmanx.h"