drm/vc4: Set TV margins on the composite connector state

[strobo5]

The overscan_* settings in the config.txt do not work on the composite video output with the VC4 KMS driver. This patch fixes it (tested on a Raspberry Pi 4). See the commit message for a more detailed description.

Here are some forum entries that I collected where people are reporting this issue:
https://forums.raspberrypi.com/viewtopic.php?t=330579
https://forums.raspberrypi.com/viewtopic.php?t=330924
https://forums.raspberrypi.com/viewtopic.php?t=342062

I did not test this with an upstream kernel, but it already does the necessary drm_atomic_helper_connector_tv_reset() in the conncetor reset function. On the other hand it does not call drm_connector_attach_tv_margin_properties() in the connector init function, which I think is necessary?!

What is the correct approach here: patch the raspberrypi kernel, then try to send a similar patch upstream?

[6by9]

This partly looks to have been fixed in mainline since 6.3 with torvalds/linux@c104b23, however I think that has missed the call to drm_connector_attach_tv_margin_properties.

Downstream has gained 745e078 in the meantime which allows the TV standard to be set via a module parameter.

I'll try to test it tomorrow to see what the state of play is in both cases. I'm happy to have a patch for it on this 6.1 branch, and we'll look at fixing mainline another day (I have a BIG pile of patches to send for Pi5 support)

[strobo5]

That sounds like a good approach to me. Thanks for looking into this. Let me know if I can help out with testing.

The margins seem to be different from the TV standard in that the comma-separated options in video= more or less directly translate into the numbers in the connector state. So my guess is that a new module parameter would not make sense here?

I'll push the commit again with my sign-off message.

[strobo5]

I couldn't stop myself from setting up a Raspberry Pi 1 with an upstream linux-6.6.2, and getting PAL output to work.

The trick was to manually set PAL mode with one of these:

modetest -M vc4 -w 50:"mode":2
modetest -M vc4 -w 50:"TV mode":3

The margins from the kernel cmdline are getting applied without further changes, thanks to drm_atomic_helper_connector_tv_reset() being called.

When I modify vc4_vec_connector_init() to do drm_connector_attach_tv_margin_properties(), the margin properties are also available to libdrm's drmModeObjectGetProperties() and can be changed with e.g.

modetest -M vc4 -w 50:"left margin":100

[6by9]

Sorry for the delay in testing this.
All looks good for this patching 6.1.

I'll sort out the patch to add drm_connector_attach_tv_margin_properties to the 6.6 kernel, and will upstream it in due course.

[6by9]

#5745 for the 6.6 fix.

6.2 to 6.5 are unlikely to get updated as they've been superceded by 6.6.

[6by9]

@popcornmix Could you cast an extra set of eyes over this one.

Upstream 6.3 gained some changes in this area, hence 6.6 needing fewer changes.

[strobo5]

Perfect, thank you!