save_vga question

["Alexander E. Patrakov" <patrakov@ums.usu.ru>]

Hello,

I am currently developing a framebuffer driver for S3 Trio 3D/2X cards. 
Well, I have a working non-accelerated driver and I am going to submit 
it later, but serious code cleanup is needed now.

I see that other fb drivers save the card state on the first open and 
restore it when the open count reaches zero. I also implemented this, 
but certainly not in the best way: by writing custom functions that save 
all CRTC, Sequencer, Graphics and Attribute VGA-like registers. I think 
that using vga_save is better here (because it also saves e.g. fonts), 
but there is a problem. Some registers of the card lock/unlock other 
registers. So the code in my custom save function looks like this (e.g. 
for Sequencer registers):

static void save_state(struct s3d2xfb_par * par)
{
    /* ... */
    u8 sr08;
    /* ... */
    sr08 = readSR(par, 0x08);
    writeSR(par, 0x06, 0x08); /* Unlock SR10-15, otherwise they are 
unreadable */
    for (i=0; i<sizeof(par->saved_SR); i++)
       par->saved_SR[i] = readSR(par, i);
    par->saved_SR[0x08] = sr08;
    writeSR(par, sr08, 0x08);
    /* ... */
}

and the corresponding code in the restore function:

static void restore_state(struct fb_info *info)
{
    int i;
    struct s3d2xfb_par *par = (struct s3d2xfb_par *) info->par;
    s3d2xfb_unlock_regs(info); /* includes a writeSR(par, sr08, 0x08); */
    /* ... */
    for (i=0; i<sizeof(par->saved_SR); i++)
       if (i!=0x08)
          writeSR(par, par->saved_SR[i], i);
    /* ... */
    writeSR(par, par->saved_SR[0x08], 0x08);
    /* ... */
}

What's the recommended way of using the save_vga() function when such 
locking problems exist? Is it acceptable to manually save the state 
necessary to restore locking (SR08 in the example above), unlock 
everything, and then save the "unlocked" state with vga_save?

-- 
Alexander E. Patrakov


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