Linux Test Case for Framebuffer Driver: C Program Example and Guide

Testing framebuffer drivers in Linux is essential for verifying the functionality of graphical output on embedded and desktop systems. A framebuffer driver manages the display’s pixel data, which is crucial for rendering graphics and UI elements. This guide provides a detailed test case for a framebuffer driver using a C program, including setup, implementation, and validation to ensure your driver performs correctly.

Understanding Framebuffer Drivers

A framebuffer driver interfaces with the display hardware to manage pixel data and control what is shown on the screen. It is responsible for rendering graphics and handling graphical input/output operations. Testing the framebuffer driver ensures that it handles these tasks correctly and efficiently.

Why Test Framebuffer Drivers?

• Functionality: Verify that the driver renders graphics and updates the display correctly.
• Performance: Ensure that the driver handles graphical operations efficiently.
• Compatibility: Test the driver across different hardware and software environments.

1. Setting Up the Test Environment

To test a framebuffer driver, you need a Linux system with the framebuffer driver installed and functional. Follow these steps to prepare your environment:

1. Install Necessary Packages:
   Ensure you have the required development tools and libraries:

   sudo apt-get update
   sudo apt-get install build-essential libdrm-dev

2. Verify Framebuffer Device:
   Check if the framebuffer device is available:

   ls /dev/fb*

You should see entries like /dev/fb0 if the framebuffer driver is installed.

2. Writing a Test Case in C

Here’s a simple C program to test the framebuffer driver. This program will fill the screen with a solid color, demonstrating basic functionality.

a. Example C Program

Save the following code as fb_test.c:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <string.h>
#include <errno.h>

#define WIDTH  800
#define HEIGHT 600

void fill_screen(unsigned int *framebuffer, unsigned int color, int width, int height) {
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            framebuffer[y * width + x] = color;
        }
    }
}

int main() {
    int fb = open("/dev/fb0", O_RDWR);
    if (fb == -1) {
        perror("Error opening framebuffer device");
        return EXIT_FAILURE;
    }

    struct fb_var_screeninfo vinfo;
    if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo)) {
        perror("Error reading variable information");
        close(fb);
        return EXIT_FAILURE;
    }

    // Map framebuffer to memory
    unsigned int *fb_ptr = mmap(0, vinfo.yres_virtual * vinfo.xres_virtual * vinfo.bits_per_pixel / 8, PROT_READ | PROT_WRITE, MAP_SHARED, fb, 0);
    if (fb_ptr == MAP_FAILED) {
        perror("Error mapping framebuffer device to memory");
        close(fb);
        return EXIT_FAILURE;
    }

    // Fill framebuffer with a solid color (e.g., red)
    fill_screen(fb_ptr, 0xFFFF0000, vinfo.xres_virtual, vinfo.yres_virtual);

    // Clean up
    munmap(fb_ptr, vinfo.yres_virtual * vinfo.xres_virtual * vinfo.bits_per_pixel / 8);
    close(fb);

    return EXIT_SUCCESS;
}

b. Compile and Run the Test

1. Compile the Program:

   gcc -o fb_test fb_test.c

2. Run the Test:

   sudo ./fb_test

This program will fill the screen with red color. Modify the fill_screen function to test other colors or patterns.

3. Validating the Test

After running the test, verify the following:

• Color Display: Check if the screen fills with the specified color.
• Error Handling: Ensure the program handles errors gracefully, such as issues with opening the framebuffer device or memory mapping.
• Performance: Observe if the framebuffer updates quickly and without significant delay.

4. Troubleshooting Common Issues

• Framebuffer Not Found: Ensure the framebuffer device exists and the driver is loaded.
• Display Issues: Verify the screen resolution and pixel format are correct.
• Permission Denied: Ensure you have sufficient permissions to access the framebuffer device (run as root if necessary).

5. Best Practices

• Test on Multiple Devices: Run tests on different hardware to ensure compatibility.
• Automate Testing: Create automated test scripts to run regularly and catch issues early.
• Document Results: Keep detailed records of test results and any issues encountered.

Conclusion

Testing a framebuffer driver is crucial for verifying that it handles graphical operations correctly. By using the provided C program example, you can test basic functionality and ensure that your driver performs as expected. Following best practices and troubleshooting common issues will help maintain reliable and efficient framebuffer drivers.