Tearing in kmscube on Pi4

[Daniel Gessel]

I modeled some kms based page flipping code on kmscube which I cloned from:

https://gitlab.freedesktop.org/mesa/kmscube.git

and see tearing on my Pi4 at the top of the screen.

So I went back to kmscube and modified the beginning of draw_cube_smooth (in cube-smooth.c) to draw a moving vertical red line and see tearing there too.

The beginning of draw_cube_smooth now looks like:

Code: Select all

static void draw_cube_smooth(unsigned i)
{
	ESMatrix modelview;

	/* clear the color buffer */
	glClearColor(0, 0, 0, 1.0);
	glClear(GL_COLOR_BUFFER_BIT);

	glEnable(GL_SCISSOR_TEST);
	glClearColor(1.0, 0, 0, 1.0);
	glScissor(i * 10 % (wd - 10), 0, 10, ht);
	glClear(GL_COLOR_BUFFER_BIT);
	glDisable(GL_SCISSOR_TEST);

Can anyone confirm this, or has anyone seen other issues with tearing, before I try to figure out how to post a bug report? Thanks!

PS: I see tearing on a Pi3 as well, but it disappears after a few seconds.

[6by9]

There is an implementation issue in FKMS at present that means we're reporting frame flip completition early. It's being investigated.

vc4-kms-v3d on a Pi3 should be clean.

[dividuum]

There is an implementation issue in FKMS at present that means we're reporting frame flip completition early. It's being investigated.

That's great to hear. This tearing issue was driving me crazy and I tried a lot of variations of my vsync code to make it work. None did so far :-O

Happy to test this once it's available.

[Daniel Gessel]

Thanks for this info. Btw, does anybody know if Kms ioctl setcrtc waits for a vblank? I was trying to use setcrtc only to have a non-vsync path but I still seem to be limited to refresh rate.

[dividuum]

There is an implementation issue in FKMS at present that means we're reporting frame flip completition early. It's being investigated.

Any hint which issue to track? Or should I open one? I guess this is an issue in the kernel, not Mesa?

[jamesh]

There is an implementation issue in FKMS at present that means we're reporting frame flip completition early. It's being investigated.

Any hint which issue to track? Or should I open one? I guess this is an issue in the kernel, not Mesa?

It could be in the VC firmware, but @6by9 would need to confirm.

[dom]

It could be in the VC firmware, but @6by9 would need to confirm.

Yes, raspberrypi/firmware is best (it is the interface between firmware and kernel, so a fix is likely to affect both).
It doesn't appear to be a mesa issue (problem not observed on vc4-kms-v3d on Pi3).

[dividuum]

It could be in the VC firmware, but @6by9 would need to confirm.

Yes, raspberrypi/firmware is best (it is the interface between firmware and kernel, so a fix is likely to affect both).
It doesn't appear to be a mesa issue (problem not observed on vc4-kms-v3d on Pi3).

Thanks dom.