vt(4): Document the new kern.vt.fb.* tunables

[dumbbell]

Summary

The new tunables allow the user to override the video mode picked for vt(4), when using a KMS driver.

[kwm]

Maybe also add example for the connector specific mode set?

share/man/man4/vt.4

220 ↗

(On Diff #2247)

to the specificed output connector

[ak]

share/man/man4/vt.4

229 ↗

(On Diff #2247)

It's not your mistake, but please add .El before ".Sh KEYBOARD SYSCTL TUNABLES".

[kwm]

comment from Avengence on IRC:
when updating vt(4) please correct the expansion of KMS (kernel mode switching -> kernel mode setting)

[dumbbell]

Changes in this new patch:

• Add examples
• Add missing .El
• Fix "Kernel Mode Setting" (was: "Kernel Mode Switching")

[dumbbell]

share/man/man4/vt.4

220 ↗

(On Diff #2247)

There's a variable name following this text, so the rendered page says:

This mode is applied to the output connector connector_name only.

[emaste]

Thank you.

We should also add some reference to methods for finding the available connectors and modes.

[dumbbell]

In D1098#9, @emaste wrote:

We should also add some reference to methods for finding the available connectors and modes.

I agree, but there's no tool that I know of to list them. And the names used by xrandr(1) don't match the expected syntax.

For Radeon users, connectors are listed in dmesg(8):

info: [drm] Radeon Display Connectors
info: [drm] Connector 0:
info: [drm]   LVDS-1
...
info: [drm] Connector 1:
info: [drm]   HDMI-A-1
...

For i915 users, nothing is logged. Perhaps they would be listed if hw.dri.debug was set, but this is only a sysctl, not a tunable. Therefore it's too late when a user can set it (I need to fix this).

For the record, here's what xrandr(1) lists on the same Radeon computer:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
LVDS connected 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
...
HDMI-0 disconnected (normal left inverted right x axis y axis)
...

And I found this out only when testing my patch, because xrandr(1) names were not working...

[dumbbell]

I believe the most useful tunable is the global one (kern.vt.fb.default_mode). But should I mention that there's no tool to list the connectors yet?

[dumbbell]

Or I simply add a log in drm2.ko for all connectors :-)

[emaste]

I would commit this now while we work on a suitable approach for enumerating connectors and modes.

[dumbbell]

Here's the result:

info: [drm] Connector LVDS-1: get mode from tunables:
info: [drm]   - kern.vt.fb.modes.LVDS-1
info: [drm]   - kern.vt.fb.default_mode
info: [drm] Connector VGA-1: get mode from tunables:
info: [drm]   - kern.vt.fb.modes.VGA-1
info: [drm]   - kern.vt.fb.default_mode

When a mode is set, DRM already tells what it found:

info: [drm] Connector LVDS-1: get mode from tunables:
info: [drm]   - kern.vt.fb.modes.LVDS-1
info: [drm]   - kern.vt.fb.default_mode
info: [drm] cmdline mode for connector LVDS-1 1024x768@60Hz
info: [drm] Connector VGA-1: get mode from tunables:
...

[dumbbell]

Changes in this new patch:

• Document how to find the connectors list
• Remove the ".Pq Kernel Mode Setting" line, because this is already explained earlier

[dumbbell]

Closed by commit rS274050 (authored by @dumbbell).

[emaste]

head/share/man/man4/vt.4

222

This should be "To discover" or "To find". But perhaps

The names of available connector names can be found in
.Xr dmesg 8
after loading the KMS driver.

225

avoid contraction

[dumbbell]

Thanks, I committed the corrections in rS274051.