Re: save_vga question

["Antonino A. Daplas" <adaplas@gmail.com>]

Alexander E. Patrakov wrote:
> 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?
> 

save_vga will only save/restore standard VGA registers, ie, in the case of the
sequencers, SR00 - SR04.  Any registers above those are extended VGA
registers, ie, their purpose depend from hardware to hardware.

So you can do it 2 ways:  One, you can save all standard VGA registers using
save_vga and save the extended VGA registers using your own function, unlocking
the locked registers, if necessary.

Another way is to set state->num_seq = 16, unlock all locked registers, then
call save_vga.

I prefer doing the first, but it's up to you.  In both case, I think it's
important to save the registers in their "unlocked" state.

Tony


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