Re: [ PATCH-LINK ] fb accel capabilities - take 2

On Sunday 30 May 2004 19:44, Thomas Winischhofer wrote:

David Eger wrote:

quoted

I'll add some comments to the patch :)

The intent for the FBINFO_HWACCEL_fnName flags is to say that the
hardware will be smart about it (i.e., it ought to be fast).  New fb
drivers have been filling in copyarea() with cfb_copyarea() (that is, the
software version) or more opaquely filling in copyarea() with their own
mydriver_copyarea(), and then conditionally calling cfb_copyarea()
depending on the noaccel flag.

Evidently.

quoted

With the patch, there are a bunch of these "is X really hardware
accelerated?" flags in fbinfo->flags, as well as FBINFO_HWACCEL_DISABLED
which should tell the driver to not use its acceleration engine --- and
use unaccelerated versions of copyarea(), fillrect(), imageblit(); and
FBINFO_MODULE (is the driver loaded as a module?)

So far so good. Can't see a reason for partly disabling acceleration,
but ok.

quoted

quoted

Erm, I wasn't aware of this. Interesting... Personally, since sisfb does
y-panning I didn't see any speed regressions compared with 2.4 yet.

So with my patch, you'd see a regression in speed until you flag that
your driver can do hardware panning.  I thought it would be good for our
small brains to put all the flags for this in one place instead of
testing the (x/y)panstep variables for zero...

There is another issue with panning. How does the new fbcon code decide
how big the virtual screen shall be (if it cares at all)? Will there be
a change in behavior?

There shouldn't be a change in behavior.  The console virtual screen 
(display->vrows) is still based on var->yres_virtual, which the driver should 
set.  fbcon also checks if var->ypanstep != 0 if the driver can do panning or 
not.  The main intent of the capability flags is choosing the best scrolling 
mode.  So in pseudo_code:

if (cannot_pan && fb_read_is_very_slow)
	no_pan + redraw;
else if (cannot_pan && fb_read_is_fast)
	no_pan + move;
else if (can_pan && fb_read_is_very_slow)
	pan + redraw;
else /* pan + fb_read_is_fast */
	pan + move;

/* an accelerated copyarea == fb_read is fast */
/* With PCI cards, fb_read is magnitudes slower than fb_write */

Of course, pan+redraw is still not supported by fbcon, so this resolves to 
no_pan + redraw.

Right now, this is more or less a hack: sisfb, unless explicitly told
not to do so (nomax or noypan), will maximize the virtual y resolution
on all var's it receives. DirectFB disables this "auto-maximizing"
feature with a respective ioctl before changing the mode etc. Works
fine. Dunno if other drivers do the same. Advantage is that users get

I think other drivers do the same.  But syntax might be different, ie (if 
var->yres_virtual == 0, then maximize var->yres_virtual, or something like 
that).

the fastest possible console by default (without using fbset or the like
to set the virtual screen size.)

Do I have to expect this mechanism to fail? IOW: (No, not io-write, in
other words ;)) Will the panning stuff change in the fbcon layer
breaking this?

quoted

quoted

Are these to set/cleared exclusively by the driver or must the driver
expect them to change? (I mean for example that fbset in 2.4 could be
used to disable acceleration, which is important to DirectFB)

The accel capability bits should be set/cleared exclusively by the driver 
depending on it's capability (duh) or if var->accel_flags is set or not.  
 

quoted

*really*?  I was wondering about that.  I'll have to go see how that
works...

Assumingly simple. Set/clears FB_ACCELF_TEXT. DirectFB uses the same
technique. Your new flags will break both.

The new flags should not break DirectFB if the driver correspondingly sets/
clears the capability bits depending on the setting of var->accel_flags.

quoted

quoted

Is there any driver already finished so that I can look it up somewhere?

There's a patch for radeonfb (my video card ;-) )

I already saw that. Will take a closer look.

quoted

quoted

Will an old driver (status as of now) work at all with the new flags not
being touched? Will it compile? (That *should* work IMHO)

/me nods.  It should. I tried compiling all of the drivers, and most of
them compiled.  The few drivers that didn't seemed to be pure 2.4 API
code that no one has loved for a long time :-/  Ah well..

(Assume you mean 2.5 API...?)

If they should compile you will need the mentioned compat-#define's in
the long run...

Thomas

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