Intel driver: increasing the maximum Xv image size

[Nicolas George]

Hi.

In i830_video.c, I read the following:

/* Limits for the overlay/textured video source sizes.  The documented hardware
 * limits are 2048x2048 or better for overlay and both of our textured video
 * implementations.  However, we run into the bigrequests limit of (currently)
 * 4MB, which even the planar format's 2048*2048*1.5 bytes is larger than.
 * Conveniently, the HD resolution, even in packed format, takes
 * (1920*1088*2) bytes, which is just shy of 4MB.  Additionally, on the 830
 * and 845, larger sizes resulted in the card hanging, so we keep the limits
 * lower there.

I was wondering what would happen if I tried to increase IMAGE_MAX_HEIGHT
from 1088 to 1200.

First, if I understand correctly git commit 6874a6f2, the hangs mentioned in
the last sentence are related to the _LEGACY versions, and not my concern
here.

As far as I understand, raising the maximum image size:

- would certainly not cause any damage to the card;

- would probably not crash the X11 server;

but:

- would allow an application to create an XvImage that would later be too
  big for XvPutImage.

And this is bad, because while XvCreateImage is an expected failure point,
that any sane application will test, XvPutImage is not expected to fail, and
that will result in a cryptic error message or an unexpected crash of the
application.

On the other hand, everything would just work fine in the following
situations:

- The image size is small enough. For example 1600×1200 < 1920×1088, so it
  would certainly work perfectly.

- For the same reason, 1920×1200 should work in planar, 12bpp mode.

- The bigrequests limit should not be a problem if XvShmPutImage is used
  instead of XvPutImage.

Well, I personally can live with cryptic error messages when I try to play
more-than-full-HD video in packed format over the network. And on the other
hand, I would like to be able to use a full screen Xv image. Therefore I
would really like to try.

But before I do something stupid, I would be very grateful for a bit of
advice from people that know what they are doing.

Regards,

-- 
  Nicolas George
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