[igt-dev] [PATCH RFC i-g-t] tests/kms_chamelium: disable output when resetting state

[Ser, Simon]

On Thu, 2019-07-11 at 14:40 +0200, Daniel Vetter wrote:
> On Thu, Jul 11, 2019 at 1:11 PM Simon Ser <simon.ser at intel.com> wrote:
> > Quoting Imre from the bug comments:
> > 
> > > If unplugging a DP-alt display while there is an active modeset on it, and
> > > then replugging the DP-alt display, the HW/FW/driver won't signal the
> > > corresponding plug-in hotplug event until the mode is disabled.
> > > 
> > > The failing tests do this:
> > > 
> > > - <have the output enabled>
> > > - unplug the display, keeping the output enabled
> > > - wait/poll for the disconnect status -> success
> > > - replug the display, while the output is still enabled
> > > - wait/poll for the connect status -> fail
> > > 
> > > This sequence is not supported with DP-alt sinks (like the USB-C to HDMI
> > > dongle), as I described above.
> > 
> > This patch changes reset_state to disable the output before unplugging the
> > connector (via chamelium_reset).
> > 
> > Signed-off-by: Simon Ser <simon.ser at intel.com>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111045
> > ---
> > 
> > This is just a RFC to check that the root issue is what we think it is.
> 
> Yeah we can't merge this, this would completely break the hotunplug
> usecase, which is:
> 1. user yanks cable
> 2. desktop reacts to hotunplug and shuts down the screen

Would disabling the screen after the drmModeConnector says it's
disconnected be better?

> If the hw can't do a hotunplug while there's an active mode, then we
> have a chicken&egg situation, and we need to resort to some form of
> polling (hooray). Hotunplug better work if the display is on.

TBH I'm not sure why it's so important to have all tests keep the mode
active during an unplug-replug sequence.

> Historical aside: Polling is disabled on may old VGA outputs because
> the polling can result in screen flickering/corruption. But hw got
> better, so even VGA managed to handle hotunplug correctly. No DE (or
> user fwiw) assumes nowadays that hotunplug is broken.
> -Daniel
> 
> >  tests/kms_chamelium.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/tests/kms_chamelium.c b/tests/kms_chamelium.c
> > index b749b5598c1d..f538ad394480 100644
> > --- a/tests/kms_chamelium.c
> > +++ b/tests/kms_chamelium.c
> > @@ -216,6 +216,13 @@ static void
> >  reset_state(data_t *data, struct chamelium_port *port)
> >  {
> >         int p;
> > +       drmModeConnector *connector;
> > +       igt_output_t *output;
> > +
> > +       connector = chamelium_port_get_connector(data->chamelium, port, false);
> > +       output = igt_output_from_connector(&data->display, connector);
> > +       igt_output_set_pipe(output, PIPE_NONE);
> > +       igt_display_commit2(&data->display, COMMIT_ATOMIC);
> > 
> >         chamelium_reset(data->chamelium);
> > 
> > --
> > 2.22.0
> > 
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> 
>