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SubjectRe: SVGA kernel chipset drivers.
On Sat, 1 Jun 1996, Tom May wrote:

> I've spliced together a few messages in which Linus writes:
>
> First, the executive summary:
>
> >The ONLY solution is X, and anything else is just noise. They should be
> >supported, but not at the cost of extra complexity in the kernel.
>
> Truly. I have worked on projects where 70% of the coding and
> debugging and testing effort required to support a board under certain
> OSs was wasted on the goddamn text-graphics-hotkey-dos-compatibilty-lcd-
> panel-virtual-device-etc bullshit! Go into graphics and stay there or
> don't go in at all.

Jesus, this isn't THAT big of a hassle! You are exaggerating.

> And if you have to read the state of the hardware back,
> in anything other than a diagnostic, that is a bad software system design.

Look there are things wrong now, and kernel video would be a
AWFULLY convenient way to deal with a lot of them in one fell swoop.
Sure, it isn't going to be a walk in the park, but it'll be worth it and
it IS doable.

> Now the rest of it:
>
> >Could we PLEASE stop this framebuffer nonsense?
> >
> >It's not going to happen. There are LOTS of cards that don't even _have_
> >framebuffers (and they are usually the really high-end ones, the ones
> >that people will want support for in the future).
>
> I feel compelled to reply that I have made my living as a display
> driver programmer for the past six or seven years and have worked on a
> lot of high-end PC video cards as a 3rd-party contractor.

Should you ever come around to our way of thinking, the GGI
project could really use someone like you.

> All the
> high-end cards that I have worked on have frame buffers. Why?
> Because you can only provide hardware acceleration for a certain
> subset of common and important operations. So when your Windows
> driver, NT driver, OS/2 driver, or X server (I've done all of these
> and more) wants to do something weird (e.g., arbitrary-size stipple on
> X, maskblt on NT, background transparency on OS/2), the easiest and
> fastest way to do it is with direct frame buffer access instead of
> trying to break a complex operation into things the card can do in
> hardware -- which may be impossible, in which case you're stuck with
> bltting a rectangle from frame buffer to memory, drawing to it, and
> bltting it back.

At the very least, it is common enough that it isn't worth
worrying about overmuch.

> >Finally, IO port acccess is not at all less critical. As far as I know,
> >there are _no_ PC graphics cards that you can really program without
> >using IO ports. Stuff like colourmaps etc are almost invariably done with
> >IO port access on PC's.
>
> I/O port access is not critical because only suboptimal cards use I/O
> ports anyway. The best way to make I/O ports faster is not to use
> them. Since at least the early 90s, good cards use memory mapping for
> everything except maybe some init functions.

[Snip]

> Anybody using a card that is I/O mapped should not complain about the
> performance -- they are using intrinsically suboptimal hardware and
> there is no reason to make hacks for it when they could be using good
> hardware and leave programmers to work on projects which advance the
> state of the art instead of holding it back.

On the other hand, one of the strong points of Linux is that is
supports even old, slow, brain-damaged hardware and pushes it as far as
it can go.

> >Trust me, we're not talking VGA here. We're talking _high_ end graphics,
> >that don't have frame-buffers because that interferes with the normal
> >mode of operations (painting the screen) for no real good reason (the
> >actual drawing is then done using screen commands and/or DMA to the card
> >to fill a area with data).
>
> Are you thinking of the XGA? That's the only card I can think of that
> uses DMA. There may have been others, I don't read the specs for
> every chip ever made, just the ones I haved worked on which is pretty
> much a who's-who list, and one or two I have evaluated. Anyway, IBM
> did all kinds of weird stuff in HW to deal with physical to virtual
> mapping and it ended up not working anyway.
>
> >> That is good enough because the virtual memory hardware can be
> >> used to make it appear to be linear. The process does not need
> >> port IO to move the window.
> >
> >Wrong. You _can_ do it that way, but if you do that then you're shooting
> >yourself in the foot. Mainly because it's horrible for performance.
>
> It's perfectly usuable. I kind of stopped doing display drivers
> because things got to the point where I thought things were fast
> enough. Nevermind that the marketing guys are still pressuring
> engineers to make things go faster -- the benchmark numbers are now
> +infinity as far as I care, meaning that once things are fast enough,
> you don't notice if they are faster. I've done some god-awful slow
> drivers that do everything in software a couple times over (I had my
> reasons) and they are still totally usable. Memory-mapping tricks +
> software drawing are certainly fast enough and require only a very
> small amount of chip-dependent code once the OS or whatever is set up
> for it. But I don't endorse such a thing because it's just a hack for
> bad hardware.

Better that than have that hardware be completely unusable, no?

Jon Taylor = <taylorj@gaia.ecs.csus.edu> | <http://gaia.ecs.csus.edu/~taylorj>
------------------------------------------------------------------------------
"Everything in excess! To enjoy the flavor of life, take big bites.
Moderation is for monks." - Lazarus Long



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