Build kernel and fbtft drivers

This guide shows how to build the kernel on the Raspberry Pi itself (takes 8-9 hours).
Cross compiling on a faster machine is possible. See http://elinux.org/RPi_Kernel_Compilation.

First Install kernel sources

Enable SPI if needed

SPI is disabled on this distro. Comment out blacklisting.

/etc/modprobe.d/raspi-blacklist.conf

#blacklist spi-bcm2708

Install fbtft

cd drivers/video/
git clone https://github.com/notro/fbtft.git

# Let make/kbuild see the directory and config options.
echo "obj-y += fbtft/" >> Makefile
sed -i 's/endmenu/source "drivers\/video\/fbtft\/Kconfig"\n\nendmenu/' Kconfig

# Make the header file available
ln fbtft/fbtft.h ../../include/linux/fbtft.h

Configure devices

For most purposes, fbtft_device can be used instead (ref: Boot console).

Make the kernel aware of the connected display.
This info is contained in arch/arm/mach-bcm2708/bcm2708.c

Add this to the include section so the structures are available:

#include <linux/fbtft.h>

Example SPI config

static struct spi_board_info bcm2708_spi_devices[] = {
	{
		.modalias = "adafruit22fb",
		.max_speed_hz = 32000000,
		.bus_num = 0,
		.chip_select = 0,
		.mode = SPI_MODE_0,
		.platform_data = &(struct fbtft_platform_data) {
			.gpios = (const struct fbtft_gpio []) {
				{ "reset", 25 },
				{ "backlight", 23 },
				{},
			},
		}
	}, {
		.modalias = "spidev",
		.max_speed_hz = 500000,
		.bus_num = 0,
		.chip_select = 1,
		.mode = SPI_MODE_0,
	}
};

Example Platform device

static struct platform_device itdb28fb_device = {
   .name = "itdb28fb",
   .id = 0,
   .dev = {
         .platform_data = &(struct fbtft_platform_data) {
            .gpios = (const struct fbtft_gpio []) {
               { "reset", 17 },
               { "dc", 1 },
               { "wr", 0 },
               { "cs", 21 },
               { "db00", 9 },
               { "db01", 11 },
               { "db02", 18 },
               { "db03", 23 },
               { "db04", 24 },
               { "db05", 25 },
               { "db06", 8 },
               { "db07", 7 },
               { "led", 4 },
               {},
            },
         },
      },
};

void __init bcm2708_init(void)
{
[snip]
	bcm_register_device(&itdb28fb_device);
[snip]
}

Configure kernel

Copy configuration from the running kernel

cd /usr/src/linux
zcat /proc/config.gz > .config

Enable fbtft in menuconfig

make menuconfig

• Device Drivers ---> Graphics support --->
• < > Support for small TFT LCD display modules (NEW) --->
  m - compiles as a loadable module
  y - copiles it into the kermel image (shown as a star *)
• Choose driver(s)

Console options

• Device Drivers ---> Graphics support ---> Console display driver support --->
  To enable rotation support for the console:

   [*]   Framebuffer Console Rotation 

By default two console fonts is available: VGA8x8 and VGA8x16
To enable more fonts:

   [*] Select compiled-in fonts
   [ ]   VGA 8x8 font (NEW)
   -*-   VGA 8x16 font
   [ ]   Mac console 6x11 font (not supported by all drivers) (NEW)
   [ ]   console 7x14 font (not supported by all drivers) (NEW)
   [ ]   Pearl (old m68k) console 8x8 font (NEW)
   [ ]   Acorn console 8x8 font (NEW)
   [ ]   Mini 4x6 font (NEW)
   [ ] Sparc console 8x16 font (NEW)
   [ ] Sparc console 12x22 font (not supported by all drivers) (NEW)
   [ ] console 10x18 font (not supported by all drivers) (NEW)

Build and install kernel/modules

# default build targets: vmlinux, modules, zImage.
# This takes between 8 and 9 hours. Overnight job?
make

# Install modules
make modules_install

# Install kernel
make zinstall

# Reboot into the new kernel
shutdown -r now