On 13.11.2013 21:20, Daniel Vetter wrote:
Thanks Daniel for your explanations. As always, very helpful.
Tile buffers aren't linear any more in memory. Tiles are 2kb in size and
are laid out in x-major direction. The tile itself is 128 bytes wide and
16 lines high. So presuming you start scanning out out at offset 0 the
dma-engine will read:
0 - 127, 2k - (2k+127), 4k - (4k+127), ... for the first display lane
128 - 255, (2k+128) - (2k+255), (4k+128) - (4k+255), ... for the 2nd display lane
...
Hmm, then there is something I don't quite understand. If I check the
code for the plane buffer start address computation, I do indeed see
something like tile addressing for GEN4 and up, but for GEN2, I simply
see a linear address = x + y * stride. This does not look consistent:
/* snip : code from i9xx_update_plane() in i915_display.c */
linear_offset = y * fb->pitches[0] + x * (fb->bits_per_pixel / 8);
if (INTEL_INFO(dev)->gen >= 4) {
intel_crtc->dspaddr_offset =
intel_gen4_compute_page_offset(&x, &y,
obj->tiling_mode,
fb->bits_per_pixel / 8,
fb->pitches[0]);
linear_offset -= intel_crtc->dspaddr_offset;
} else {
intel_crtc->dspaddr_offset = linear_offset;
}
/* snip */
Are you *really sure* GEN2 does have tiling? Or could it be that this
bit is used for something else and probably turns on some weird
powersaving feature that creates some mischief with the FIFO? After all,
a tile cannot always be 128 pixels long independent of the display
organization (i.e. "pixel format") *and* have the above formula correct?
There is then at least something I must be missing.
I wonder how that works in windows, though. The intel driver does
support panning to some degree, at least if the resolutions of the
internal and external display differ.
Could be that windows scrolls in software by copying the buffer around.
Maybe the tearfree option can help here, although I expect it to hurt
badly for gtt constrained i830M platforms. And tbh I don't know whether it
works with panning.
Actually, scrolling is quite smooth, I doubt it's a software scrolling.
But anyhow...
Greetings,
Thomas
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