Re: my opinion about VGA devices

[Tomas Carnecky]

Richard B. Johnson wrote:

> On ix86 machines, regardless of whatever code initialized the
> hardware, if the screen-card is not put into graphics mode,
> anybody can write characters and attributes at 0xb8000 directly
> to the screen. Even user-mode code can mmap() that area and write
> to it. So, the key seems to be to get out of graphics mode
> before suspend, and go back later after resume.

Why do you let user-mode programs access the hardware directly?
You don't do this with network devices (there you have syscalls), you 
don't do this with sound devices (alsa).
IMO it makes a proper power managment implementation impossible.

You can say that there are two different drivers for screen-cards in the 
kernel. One is the VGA which enables the card during early boot time to 
display the first text messages and the other is fb/DRI or even an 
nvidia/ati kernel module which is enabled later on.
Last time I've tried a LiveCD distro I've seen a nice boot console with 
background picture, high resolution (1024x768) and nice small font. That 
means that the framebuffer driver had to be initialized at that time. I 
don't have framebuffer drivers compiled into my kernel so I don't know 
at which point these are initialized, but it must be at a quite early 
point in the boot process.
When looking at the output of dmesg I can see that the first thing that 
is initialized are the CPU's, ACPI, IRQ's and then the PCI bus is 
scanned. Did anyones machine crash during these steps? I don't think a 
healthy box will crash here. And at this point you can initialize your 
graphics card driver like it is done in the LiveCD distro.

tom
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