Enable RP1 PIO driver and add notes

This will enable some pretty cool I/O on the RPi5 for those interested
in programming the PIO state machines.

Author: fhunleth

README.md

@@ -76,6 +76,16 @@ cmd("amixer cset numid=3 2")
 
 Change the last argument to `amixer` to `1` to output to the stereo output jack.
 
+## RP1 PIO
+
+The `rpi1-pio` device driver allows use of the PIO hardware using
+[`piolib`](https://github.com/raspberrypi/utils/tree/master/piolib). If you
+don't see `/dev/pio0`, the most likely cause is that you need to update your
+Raspberry Pi's boot EEPROM. See
+[rpi-eeprom](https://github.com/raspberrypi/rpi-eeprom) for binaries. It may be
+easier to upgrade the EEPROM via RaspberryPi OS if the instructions aren't
+clear.
+
 ## Provisioning devices
 
 This system supports storing provisioning information in a small key-value store

linux-6.6.defconfig

@@ -160,6 +160,7 @@ CONFIG_RASPBERRYPI_FIRMWARE=y
 CONFIG_OF_CONFIGFS=y
 CONFIG_BLK_DEV_LOOP=y
 CONFIG_BLK_DEV_RAM=y
+CONFIG_RP1_PIO=y
 CONFIG_EEPROM_AT24=m
 CONFIG_SCSI=y
 # CONFIG_SCSI_PROC_FS is not set
@@ -274,7 +275,6 @@ CONFIG_INPUT_EVDEV=y
 # CONFIG_INPUT_KEYBOARD is not set
 # CONFIG_INPUT_MOUSE is not set
 CONFIG_INPUT_JOYSTICK=y
-CONFIG_JOYSTICK_RPISENSE=m
 CONFIG_INPUT_TOUCHSCREEN=y
 CONFIG_TOUCHSCREEN_EDT_FT5X06=m
 CONFIG_TOUCHSCREEN_RASPBERRYPI_FW=m
@@ -476,6 +476,7 @@ CONFIG_COMMON_CLK_RP1_SDIO=y
 CONFIG_CLK_RASPBERRYPI=y
 CONFIG_MAILBOX=y
 CONFIG_BCM2835_MBOX=y
+CONFIG_MBOX_RP1=y
 CONFIG_BCM2712_IOMMU=y
 CONFIG_RASPBERRYPI_POWER=y
 CONFIG_PWM=y