bug in matrox fb vsync code

I tried to mail this to Petr Vandrovec <[email protected]> but the domain does not resolve.

I'm using kernel 2.4.18, and noticed a bug in the matrox vsync code... Here's drivers/video/matrox/matroxfb_base.c from line 992 onwards:

    static int matroxfb_get_vblank(CPMINFO struct fb_vblank *vblank)
    {
        unsigned int sts1;
    
        memset(vblank, 0, sizeof(*vblank));
        vblank->flags = FB_VBLANK_HAVE_VCOUNT | FB_VBLANK_HAVE_VSYNC |
                FB_VBLANK_HAVE_VBLANK | FB_VBLANK_HAVE_HBLANK;
        sts1 = mga_inb(M_INSTS1);
        vblank->vcount = mga_inl(M_VCOUNT);
        /* BTW, on my PIII/450 with G400, reading M_INSTS1
           byte makes this call about 12% slower (1.70 vs. 2.05 us
           per ioctl()) */
        if (sts1 & 1)
            vblank->flags |= FB_VBLANK_HBLANKING;
        if (sts1 & 8)
            vblank->flags |= FB_VBLANK_VSYNCING;
****    if (vblank->count >= ACCESS_FBINFO(currcon_display)->var.yres)
            vblank->flags |= FB_VBLANK_VBLANKING;
        vblank->hcount = 0;
        vblank->count = 0;
        return 0;
    }

The line in question (marked ****) reads from vblank->count which is zeroed by the memset and not changed since then. I believe it should be reading from vblank->vcount instead.

I'm sorry not to have checked whether this has been fixed; I found that some Matrox bugs were fixed since 2.4.18 in the 2.4.19 prerelease changelog, but my Internet connection is only a 56k modem so I can't afford to download either the prerelease patch or the latest development branch.

I'd also be interested to know if there's any documentation of the difference between VSYNC and VBLANK in the context of the fbdev code -- I haven't found any references in the kernel documentation, perhaps there's some resource online?

Thanks for your time,

George

It should be vblank->vcount. It is fixed in mga-2.5.20-tvout.gz at ftp://platan.vc.cvut.cz/pub/linux/matrox-latest. Obviously this patch does not apply to 2.4.x.

Yes.

AFAIK it is not fixed even in latest 2.4.x prepatches.

linux-fbdev.sourceforge.net maybe have some documentation. I wrote implementation according to flags names...
Petr Vandrovec [email protected]