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notro edited this page Sep 20, 2013 · 18 revisions

This is a step-by-step guide showing how to add and compile a new FBTFT driver in 30 minutes.

This doesn't work with the rpi-update release. See issue

This guide can also be used to get the latest driver update, if a new image hasn't been released yet.
Follow the guide and skip the example driver.

See this for an overview: How-it-works

If you want to contribute code, see Submitting patches

Boot with the latest FBTFT image.

Expand the root file system size.

sudo raspi-config
# expand_rootfs

Install dependencies

sudo apt-get update
sudo apt-get -y install git libncurses5-dev

Samba (optional)

Samba can be used to aid development on the Pi.

sudo apt-get -y install samba samba-common-bin

sudo cp /etc/samba/smb.conf /etc/samba/smb.conf.org


sudo sed -i '/ Share Definitions /q' /etc/samba/smb.conf

cat <<EOF | sudo tee -a /etc/samba/smb.conf

[homes]
   comment = Home Directories
   browseable = no
   read only = no
   create mask = 0644
   directory mask = 0755
   valid users = %S

EOF

sudo service samba restart
sudo smbpasswd -a pi

Home directory for user pi will be available at \\xxx.xxx.xxx.xxx\pi

Source

We don't need the complete git history (--depth 1). This will speed things up considerly.

cd
git clone --depth 1 git://github.com/raspberrypi/linux.git

fbtft source

cd ~/linux/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

Preparation

cp ~/extra/{.config,Module.symvers} ~/linux/

cd ~/linux
make prepare scripts

Build

Lets make sure it builds before we start changing things.

This can be run from any directory

make -C /lib/modules/$(uname -r)/build SUBDIRS=drivers/video/fbtft modules

If config asks if it should build FB drivers, answer m for module.

If you are just building the latest source and not adding a driver or display, skip to Install

Example driver: fb_hello

This shows how to add a new driver for the Hello LCD Controller.

Add to ~/linux/drivers/video/fbtft/Kconfig

config FB_TFT_HELLO
        tristate "Example FBTFT driver"
        depends on FB_TFT

Add to ~/linux/drivers/video/fbtft/Makefile

obj-$(CONFIG_FB_TFT_HELLO)       += fb_hello.o

Create ~/linux/drivers/video/fbtft/fb_hello.c

/*
 * Copyright and GPL statement
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/delay.h>

#include "fbtft.h"

#define DRVNAME		"fb_hello"
#define WIDTH		128
#define HEIGHT		128

static int init_display(struct fbtft_par *par)
{
	fbtft_par_dbg(DEBUG_INIT_DISPLAY, par, "%s()\n", __func__);

	printk("Hello World");

	return 0;
}

static void set_addr_win(struct fbtft_par *par, int xs, int ys, int xe, int ye)
{
	fbtft_par_dbg(DEBUG_SET_ADDR_WIN, par,
		"%s(xs=%d, ys=%d, xe=%d, ye=%d)\n", __func__, xs, ys, xe, ye);

}

static struct fbtft_display display = {
	.regwidth = 8,
	.width = WIDTH,
	.height = HEIGHT,
	.fbtftops = {
		.init_display = init_display,
		.set_addr_win = set_addr_win,
	},
};
FBTFT_REGISTER_DRIVER(DRVNAME, &display);

/*
    This makes the driver autoload if the device is present
    modprobe will load it from /lib/modules and not the build directory
	If your driver changes doesn't come into effect, this could be why
*/
MODULE_ALIAS("spi:" DRVNAME);
MODULE_ALIAS("platform:" DRVNAME);

MODULE_DESCRIPTION("FB driver for the Hello LCD Controller");
MODULE_AUTHOR("Me");
MODULE_LICENSE("GPL");

Example display: hello

This shows how to add a device for the Hello 1.5 inch display, which uses the SPI bus.

Add to static struct fbtft_device_display displays[] in file ~/linux/drivers/video/fbtft/fbtft_device.c

	}, {
		.name = "hello15",
		.spi = &(struct spi_board_info) {
			.modalias = "fb_hello",
			.max_speed_hz = 32000000,
			.mode = SPI_MODE_0,
			.platform_data = &(struct fbtft_platform_data) {
				.display = {
					.buswidth = 8,
				},
				.bgr = true,
				.gpios = (const struct fbtft_gpio []) {
					{ "reset", 25 },
					{ "dc", 24 },
					{},
				},
			}
		}

Configure

Start kernel configuration program

cd ~/linux
make menuconfig

Enable fb_hello

Device Drivers  ---> Graphics support  --->  Support for small TFT LCD display modules  --->

<M>   Example FBTFT driver

make prepare

Now rerun the previous build step.

Test

sudo dmesg -C
sudo modprobe fbtft
sudo insmod ~/linux/drivers/video/fbtft/fb_hello.ko
sudo insmod ~/linux/drivers/video/fbtft/fbtft_device.ko name=hello15 debug=3
dmesg

fbtft_device:  SPI devices registered:
fbtft_device:      spidev spi0.1 500kHz 8 bits mode=0x00
fbtft_device:  'fb' Platform devices registered:
fbtft_device:      bcm2708_fb id=-1 pdata? no

fb_hello spi0.0: fbtft_request_gpios: 'reset' = GPIO25
fb_hello spi0.0: fbtft_request_gpios: 'dc' = GPIO24
fb_hello spi0.0: fbtft_verify_gpios()
fb_hello spi0.0: init_display()
Hello World
fb_hello spi0.0: Elapsed time for display update:   21.914092 ms (fps: 45, lines=128)
graphics fb1: fb_hello frame buffer, 128x128, 32 KiB video memory, 4 KiB buffer memory, fps=20, spi0.0 at 32 MHz

fbtft_device:  GPIOS used by 'hello15':
fbtft_device:    'reset' = GPIO25
fbtft_device:    'dc' = GPIO24
fbtft_device:  SPI devices registered:
fbtft_device:      spidev spi0.1 500kHz 8 bits mode=0x00
fbtft_device:      fb_hello spi0.0 32000kHz 8 bits mode=0x00

sudo rmmod fb_hello fbtft_device fbtft

Install

# install the new driver
sudo cp /lib/modules/$(uname -r)/build/drivers/video/fbtft/{fbtft_device.ko,fb_hello.ko} /lib/modules/$(uname -r)/kernel/drivers/video/fbtft/
sudo depmod

# update all drivers/modules
sudo cp -v /lib/modules/$(uname -r)/build/drivers/video/fbtft/*.ko /lib/modules/$(uname -r)/kernel/drivers/video/fbtft/
sudo depmod

sudo modprobe fbtft_device name=hello15 debug=3

Submitting patches

I you want me to include your driver, follow these rules:

  • The license the code is released under has to be GPL version 2 or later. Add this information at the top of the file.

  • Agree with the Developer's Certificate of Origin 1.1 (12. Sign your work)

  • Follow the Linux kernel coding style
    Use linux/scripts/checkpatch.pl --file fb_xxx.c to verify your code.
    Lines can exceed 80 columns if the meaning is hard to grasp when breaking up the line. Never exceed 132 columns.

  • Make an issue and include your driver in a code block for review.

  • When the driver is approved, I can just copy the code from the issue, or you can make a pull request with just one commit in it. If I commit the driver directly from the issue, a Signed-off-by line will be added to the commit message to credit the author.

Except for trivial patches, make an issue first before making a pull request too see if I agree with you. Only one fix/feature per commit and vice versa. I can commit simple changes directly from an issue, a pull request is not needed.

Kernel messages in SSH session

When doing development and testing from a SSH session, it's nice to see the that kernel panic message before everything freezes.

Make file /etc/rsyslog.d/kern_pi.conf with contents:

kern.err  pi

This will show kernel error messages and worse when user pi is logged in.

service rsyslog restart

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