Is framebufer driver a replacement for video driver?

Is framebufer driver a replacement for video driver?

[Mukund JB.]

Hi all,

I have a small query. I may be silly, but please help by make it clear.

Framebuffer definition :-

The frame buffer device provides an abstraction for the graphics
hardware. It represents the frame buffer of some video hardware and
allows application software to access the graphics hardware through a
well-defined interface, so the software doesn't need to know anything
about the low-level (hardware register) stuff.

Does a framebuffer driver directly interact with the hardware registers
of the video card? 
					or 

Is there a generic low level driver that will interact with the
hardware?

What happens when I say startx at command prompt with XF86Config-4 file
configured for framebuffer driver?

Is it like, When I say startx with XF86Config-4 file configured for
framebuffer driver, the video we get is a result of X server using the
framebuffer driver directly? Right?

In this case, Is there a video driver involved in getting the video
apart from the framebuffer driver?

Thanks for the linux society for the continues support.

Regards,
Mukund jampala



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Re: Is framebufer driver a replacement for video driver?

[Antonino A. Daplas]

On Friday 05 November 2004 00:29, Mukund JB. wrote:
> Hi all,
>
> I have a small query. I may be silly, but please help by make it clear.
>
> Framebuffer definition :-
>
> The frame buffer device provides an abstraction for the graphics
> hardware. It represents the frame buffer of some video hardware and
> allows application software to access the graphics hardware through a
> well-defined interface, so the software doesn't need to know anything
> about the low-level (hardware register) stuff.
>
> Does a framebuffer driver directly interact with the hardware registers
> of the video card?

Yes.

> 					or
>
> Is there a generic low level driver that will interact with the
> hardware?

Yes and No. Yes, because there are platform drivers that may work with
many cards (VESA, VGA16, OF).  You can consider them as generic.

However, the hardware specific specific driver will work only with a
particular chipset.

>
> What happens when I say startx at command prompt with XF86Config-4 file
> configured for framebuffer driver?
>
> Is it like, When I say startx with XF86Config-4 file configured for
> framebuffer driver, the video we get is a result of X server using the
> framebuffer driver directly? Right?
>

Yes.

> In this case, Is there a video driver involved in getting the video
> apart from the framebuffer driver?
>

The framebuffer driver itself touches the hardware, and usually it's one
driver per chipset.  However, the interface that is used by the application
is standard.

Tony




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RE: Is framebufer driver a replacement for video driver?

[Mukund JB.]

Hi Adaplas,

> > I have a small query. I may be silly, but please help by make it
clear.
> >
> > Framebuffer definition :-
> >
> > The frame buffer device provides an abstraction for the graphics
> > hardware. It represents the frame buffer of some video hardware and
> > allows application software to access the graphics hardware through
a
> > well-defined interface, so the software doesn't need to know
anything
> > about the low-level (hardware register) stuff.
> >
> > Does a framebuffer driver directly interact with the hardware
registers
> > of the video card?
> Yes.
>
> > 					or
> >
> > Is there a generic low level driver that will interact with the
> > hardware?
> 
> Yes and No. Yes, because there are platform drivers that may work with
> many cards (VESA, VGA16, OF).  You can consider them as generic.

Are you talking about the vesafb driver? this being  a generic driver,
Will this driver work on any video card? 
If a card is VESA 2.0 complaint, is there a generic framebuffer driver
that will work on it? 

I assume VESA 2.0 standards will define hardware registers.

> However, the hardware specific specific driver will work only with a
> particular chipset.

What chages from framebuffer driver to framebuffer driver?
I think its just hardware accessing.

> >
> > What happens when I say startx at command prompt with XF86Config-4
file
> > configured for framebuffer driver?
> >
> > Is it like, When I say startx with XF86Config-4 file configured for
> > framebuffer driver, the video we get is a result of X server using
the
> > framebuffer driver directly? Right?
> >
> 
> Yes.
> 
> > In this case, Is there a video driver involved in getting the video
> > apart from the framebuffer driver?
> >
> 
> The framebuffer driver itself touches the hardware, and usually it's
one
> driver per chipset.  However, the interface that is used by the
> application
> is standard.

Let's make this clearer.
The video I get after startx is running just on framebuffer driver?
There is no other video driver involved in the running video.right?


Thanks for ur response.

Regards,
Mukund jampala



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RE: Is framebufer driver a replacement for video driver?

[Geert Uytterhoeven]

On Fri, 5 Nov 2004, Mukund JB. wrote:
> > > Is there a generic low level driver that will interact with the
> > > hardware?
> > 
> > Yes and No. Yes, because there are platform drivers that may work with
> > many cards (VESA, VGA16, OF).  You can consider them as generic.
> 
> Are you talking about the vesafb driver? this being  a generic driver,
> Will this driver work on any video card? 

Yep, `VESA' means the vesafb driver. It works on any video card with a VESA 2.0
compliant BIOS.

> If a card is VESA 2.0 complaint, is there a generic framebuffer driver
> that will work on it? 
> 
> I assume VESA 2.0 standards will define hardware registers.

No, it's a BIOS standard. It standardizes how to talk to the BIOS to set a
(linear) graphics mode.

> > However, the hardware specific specific driver will work only with a
> > particular chipset.
> 
> What chages from framebuffer driver to framebuffer driver?
> I think its just hardware accessing.

Yep. But the way you program the graphics chip may differ a lot among different
graphics chips.

> > > What happens when I say startx at command prompt with XF86Config-4
> file
> > > configured for framebuffer driver?
> > >
> > > Is it like, When I say startx with XF86Config-4 file configured for
> > > framebuffer driver, the video we get is a result of X server using
> the
> > > framebuffer driver directly? Right?
> > >
> > 
> > Yes.
> > 
> > > In this case, Is there a video driver involved in getting the video
> > > apart from the framebuffer driver?
> > >
> > 
> > The framebuffer driver itself touches the hardware, and usually it's
> one
> > driver per chipset.  However, the interface that is used by the
> > application
> > is standard.
> 
> Let's make this clearer.
> The video I get after startx is running just on framebuffer driver?
> There is no other video driver involved in the running video.right?

For unaccelerated operation, yes.

If you want hardware accelerated drawing operations, the X server still has to
known how to program the graphics chip. The frame buffer device takes care
about setting the video mode and color palette, and mapping video RAM only.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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RE: Is framebufer driver a replacement for video driver?

[Mukund JB.]

Hi Geert,

Thanks for that.
Please, try to give me more clarity on the framebuffer driver by solving
the below quires?

> > Are you talking about the vesafb driver? This being  a generic
driver,
> > Will this driver work on any video card?
> 
> Yep, `VESA' means the vesafb driver. It works on any video card with a
> VESA 2.0
> compliant BIOS.

If vesafb module works for any card, what are the situations that make
me write a new framebuffer driver for a new video hardware in the
market?

Is it like, the vesafb driver does not explore the card to the fullest
extent? 
A framebuffer driver specific to Video card is just to explore the card
features to maximum.

Can u please tell me why to call "scr_readw" in accel.c file of riva
directory doing?
Also, I found NO readl, writel calls in the riva directory( framebuffer
driver). Then, who is responsible for accessing the hardware here?

> > Let's make this clearer.
> > The video I get after startx is running just on framebuffer driver?
> > There is no other video driver involved in the running video.right?
> 
> For unaccelerated operation, yes.

If accelerated operation is needed, then do we need video driver (nv for
nvidia card) apart from the framebuffer driver to manage the video?

> If you want hardware accelerated drawing operations, the X server
still
> has to
> known how to program the graphics chip. The frame buffer device takes
care
> about setting the video mode and color palette, and mapping video RAM
> only.

My question in this regard is : 
Is there a video driver involved apart from the framebuffer driver why I
get the video from the startx command?

Ohh, Do u mean, to program the graphics chip in case of accelerated
operations we need a video driver apart from the framebuufer driver?
If so, is framebuffer driver not capable of programming the graphic card
for accelerated operations?


My assumption about framebuffer driver architecture is:

	X SERVER
-----------------
FRAMEBUFFER DRIVER
-----------------
HARDWARE ( VIDEO CARD)
-----------------

Please correct my assumptions if u find them faulty.
Thanks for ur support.

Regards,
Mukund jampala



> > > > Is there a generic low level driver that will interact with the
> > > > hardware?
> > >
> > > Yes and No. Yes, because there are platform drivers that may work
with
> > > many cards (VESA, VGA16, OF).  You can consider them as generic.
> >
> > Are you talking about the vesafb driver? this being  a generic
driver,
> > Will this driver work on any video card?
> 
> Yep, `VESA' means the vesafb driver. It works on any video card with a
> VESA 2.0
> compliant BIOS.
> 
> > If a card is VESA 2.0 complaint, is there a generic framebuffer
driver
> > that will work on it?
> >
> > I assume VESA 2.0 standards will define hardware registers.
> 
> No, it's a BIOS standard. It standardizes how to talk to the BIOS to
set a
> (linear) graphics mode.
> 
> > > However, the hardware specific specific driver will work only with
a
> > > particular chipset.
> >
> > What chages from framebuffer driver to framebuffer driver?
> > I think its just hardware accessing.
> 
> Yep. But the way you program the graphics chip may differ a lot among
> different
> graphics chips.
> 
> > > > What happens when I say startx at command prompt with
XF86Config-4
> > file
> > > > configured for framebuffer driver?
> > > >
> > > > Is it like, When I say startx with XF86Config-4 file configured
for
> > > > framebuffer driver, the video we get is a result of X server
using
> > the
> > > > framebuffer driver directly? Right?
> > > >
> > >
> > > Yes.
> > >
> > > > In this case, Is there a video driver involved in getting the
video
> > > > apart from the framebuffer driver?
> > > >
> > >
> > > The framebuffer driver itself touches the hardware, and usually
it's
> > one
> > > driver per chipset.  However, the interface that is used by the
> > > application
> > > is standard.
> >
> > Let's make this clearer.
> > The video I get after startx is running just on framebuffer driver?
> > There is no other video driver involved in the running video.right?
> 
> For unaccelerated operation, yes.
> 
> If you want hardware accelerated drawing operations, the X server
still
> has to
> known how to program the graphics chip. The frame buffer device takes
care
> about setting the video mode and color palette, and mapping video RAM
> only.
> 
> Gr{oetje,eeting}s,
> 
> 						Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a
hacker.
> But
> when I'm talking to journalists I just say "programmer" or something
like
> that.
> 							    -- Linus
Torvalds
> 
> 
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RE: Is framebufer driver a replacement for video driver?

[Geert Uytterhoeven]

On Fri, 5 Nov 2004, Mukund JB. wrote:
> > > Are you talking about the vesafb driver? This being  a generic
> driver,
> > > Will this driver work on any video card?
> > 
> > Yep, `VESA' means the vesafb driver. It works on any video card with a
> > VESA 2.0
> > compliant BIOS.
> 
> If vesafb module works for any card, what are the situations that make
> me write a new framebuffer driver for a new video hardware in the
> market?
>
> Is it like, the vesafb driver does not explore the card to the fullest
> extent? 
> A framebuffer driver specific to Video card is just to explore the card
> features to maximum.

Yes.

Limitations of vesafb:
  - Since the video mode must be changed by calling the BIOS, vesafb cannot
    change the video mode after boot up (the video mode is set just _before_
    the Linux kernel is started).
  - Limited to the video modes (and refresh rates) in the BIOS.
  - No text console acceleration.

A `native' driver removes these limitations.

> Can u please tell me why to call "scr_readw" in accel.c file of riva
> directory doing?

scr_readw() is used to read the data (character value + attributes) for a text
mode character cell from the shadow screen that is used to implement virtual
consoles.

> Also, I found NO readl, writel calls in the riva directory( framebuffer
> driver). Then, who is responsible for accessing the hardware here?

Probably rivafb still accesses the hardware by direct pointer manipulation,
which is not portable.

> > > Let's make this clearer.
> > > The video I get after startx is running just on framebuffer driver?
> > > There is no other video driver involved in the running video.right?
> > 
> > For unaccelerated operation, yes.
> 
> If accelerated operation is needed, then do we need video driver (nv for
> nvidia card) apart from the framebuffer driver to manage the video?

Yes. But I don't know whether nv supports that mode of operation.

> > If you want hardware accelerated drawing operations, the X server
> still
> > has to
> > known how to program the graphics chip. The frame buffer device takes
> care
> > about setting the video mode and color palette, and mapping video RAM
> > only.
> 
> My question in this regard is : 
> Is there a video driver involved apart from the framebuffer driver why I
> get the video from the startx command?
> 
> Ohh, Do u mean, to program the graphics chip in case of accelerated
> operations we need a video driver apart from the framebuufer driver?

You need a chipset-specific driver to issue drawing commands to the
acceleration engine. The frame buffer device provides an abstraction for the
frame buffer (= bunch of memory that represents the screen image) only.

> If so, is framebuffer driver not capable of programming the graphic card
> for accelerated operations?

Indeed. The sole exception is in-kernel accelerated drawing to increase the
emulated text console performance.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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Re: Is framebufer driver a replacement for video driver?

[Antonino A. Daplas]

On Friday 05 November 2004 19:44, Mukund JB. wrote:
> Hi Geert,
>
> Thanks for that.
> Please, try to give me more clarity on the framebuffer driver by solving
> the below quires?
>
> > > Are you talking about the vesafb driver? This being  a generic
>
> driver,
>
> > > Will this driver work on any video card?
> >
> > Yep, `VESA' means the vesafb driver. It works on any video card with a
> > VESA 2.0
> > compliant BIOS.
>
> If vesafb module works for any card, what are the situations that make
> me write a new framebuffer driver for a new video hardware in the
> market?
>
> Is it like, the vesafb driver does not explore the card to the fullest
> extent?
> A framebuffer driver specific to Video card is just to explore the card
> features to maximum.
>
> Can u please tell me why to call "scr_readw" in accel.c file of riva
> directory doing?
> Also, I found NO readl, writel calls in the riva directory( framebuffer
> driver). Then, who is responsible for accessing the hardware here?
>

Because the supposedly OS-agnostic file uses direct pointer manipulation, which
does imply that this file is not trully OS-agnostic.

The rivafb in 2.6.10-rc1-mm3 is already ported to use readl/writel.
.
Tony




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