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Frame buffer double buffer?

Steven Weng1
Expert 2200 points


Hi Tis,

I am using DM8168 and DVRRDK v4.1. Does frame buffer support double buffer feature?

Here is some codes to use frame buffer ioctl for getting fixed screen info and variable screen info...

    // open fb device
    fb->fd = open("/dev/fb0", O_RDWR);
    if (fb->fd < 0)
    {
        LOG_ERR("[bootfb] Can't open frame buffer device!\n");
        return -1;
    }

    // get screen's fixed info
    if (ioctl(fb->fd, FBIOGET_FSCREENINFO, &fb->finfo) < 0)
    {
        LOG_ERR("[bootfb] Read fixed screen info failed!\n");
        return -1;
    }

    // get screen's var info
    if (ioctl(fb->fd, FBIOGET_VSCREENINFO, &fb->vinfo) < 0)
    {
        LOG_ERR("[bootfb] Read variable screen information failed!\n");
        return -1;
    }

...

I print resolution of VSCREENINFO as below:

fb->vinfo.xres = 1920, fb->vinfo.yres = 1080, fb->vinfo.xres_virtual = 1920, fb->vinfo.yres_virtual = 1080

But after I modify the fb->vinfo.yres_virtual = 2160 and use FBIOPUT_VSCREENINFO ioctl to apply the new parameter...

There is no error after set FBIOPUT_VSCREENINFO but the vinfo.yres_virtual is still the same 1080...not 2160.

Why?

BR,

Steven

  • 0
    TI__Guru**** 484335 points
    It really depends on the buffer allocated and output resolution. If you have allocated/provided enough buffer size at the time of insertion of fbdev driver, you should be able to do double buffering.
    Rgds,Brijesh
  • 0 in reply to Brijesh Jadav
    Expert 2200 points

    Hi Brijesh,
    thanks for your quickly reply.

    I want display 1920x1080 frame buffer. RGBA raw data 1920x1080x4 = 8294400.
    I have modified the following vram parameter of fb0 to 16MB:
    insmod ./kermod/ti81xxfb.ko vram=0:16M,1:8M,2:8M
    But the result is the same. Am I missing something?
    Thanks!
    BR,
    Steven

  • 0 in reply to Steven Weng1
    TI__Guru**** 484335 points
    i dont see anywhere it getting reset.
    The only place where it will be reset, is in below code.
    if (line_size * var->yres_virtual > tfbi->mreg.size) {
    TFBDBG("can't fit fb memory, reducing y\n");
    var->yres_virtual = tfbi->mreg.size / line_size;
    If the line size and vertual height is more than allocated memory, then it will get reset to size/line size. can you again check the memory size.
    Rgds,Brijesh
  • 0 in reply to Brijesh Jadav
    Expert 2200 points

    Hi Brijesh,

    Sorry for late reply.

    There are some hard code in DVRRDK ti81xxfb driver. So the vrams parameter is useless when insmod the module.

    if (def_vram && ti81xxfb_parse_vram_param(def_vram, TI81XX_FB_NUM,
             vrams)) {
            dev_err(fbdev->dev,
            "failed to parse vram parameters: %s\n", def_vram);

            memset(vrams, 0, sizeof(vrams));
        }
        /*#if defined(CONFIG_MACH_UD8168_DVR)
        else {    //# phoong : fixed vram size of fb (default)
            vrams[0] = 0x7E9000;    //# 8M (1920x1080x4, 0x7E9000)
            vrams[1] = 0x7E9000;    //# 8M (1920x1080x4, 0x7E9000)
            vrams[2] = 0x400000;    //# 4M (720x480(1080)x4, 0x151800(0x2F7600))
        }

    Thanks for your help!

    BR,

    Steven