Is there the possibility to support EXA for legacy S3 chips?

[Alex Deucher]

On Wed, May 27, 2009 at 6:20 PM, Ville Syrjälä <syrjala at sci.fi> wrote:
> On Wed, May 27, 2009 at 05:50:51PM -0400, Alex Deucher wrote:
>> On Wed, May 27, 2009 at 5:09 PM, Evgeny M. Zubok <evgeny.zubok at tochka.ru> wrote:
>> >
>> > I have made the first attempt to implement basic `Copy' and `Solid' EXA
>> > functions in xf86-video-s3, but soon came to intention that EXA support
>> > is not possible. Is there mistake in my thinking below?
>> >
>> > S3's Graphic Processor (S3 GP) is able to copy areas only in terms of
>> > coordinates, i. e. it can copy rectangle from (src-x, src-y) to (dest-x,
>> > dest-y) with width w and height h (Fig. 1). This method is used in XAA
>> > ScreenToScreenCopy function. But S3 GP hasn't mean to copy offscreen
>> > pixmaps in format presented on Fig. 2 to framebuffer, i. e. there is no
>> > way to write the pixmap's offset and pitch directly into GP registers to
>> > make subsequent copying. I looked up on the code of few other drivers
>> > where EXA is implemented (ati, trident, mga) -- all these chips have the
>> > possibility to write offset and pitch of pixmap into their GP.
>> >
>> > Although the method (by means of Pixel Transfer Register) exists to
>> > upload pixmap from the system memory to S3's offscreen memory in
>> > required format (Fig. 1) (I didn't try it), such offscreen memory
>> > organization will not be understandable to the EXA offscreen memory
>> > manager. Most probably this will follow to incorrect pixmap migration
>> > and overwriting previously uploaded pixmaps.
>> >
>> > The objection above sounds like the judgement to EXA support in S3
>> > driver. No?
>>
>> Looks like no dice for EXA.  Fixed pitches, no offsets... ouch.
>
> Why wouldn't it work if you just allocate everything using the same
> pitch? Or does the allocator make some assumptions about the pitches the
> hardware can handle?

The allocator doesn't support a fixed pitch, only pitch alignment.
You could probably hack something together and disable offscreen
pixmaps, but I don't think it would be worth the effort as you'd
probably end up falling back in a lot of cases and the lack offscreen
pixmaps would hurt performance.

Alex