[PATCH v3 032/105] drm/vc4: crtc: Enable and disable the PV in atomic_enable / disable

[Eric Anholt]

On Tue, Jun 2, 2020 at 8:02 AM Dave Stevenson
<dave.stevenson at raspberrypi.com> wrote:
>
> Hi Maxime and Eric
>
> On Tue, 2 Jun 2020 at 15:12, Maxime Ripard <maxime at cerno.tech> wrote:
> >
> > Hi Eric
> >
> > On Wed, May 27, 2020 at 09:54:44AM -0700, Eric Anholt wrote:
> > > On Wed, May 27, 2020 at 8:50 AM Maxime Ripard <maxime at cerno.tech> wrote:
> > > >
> > > > The VIDEN bit in the pixelvalve currently being used to enable or disable
> > > > the pixelvalve seems to not be enough in some situations, which whill end
> > > > up with the pixelvalve stalling.
> > > >
> > > > In such a case, even re-enabling VIDEN doesn't bring it back and we need to
> > > > clear the FIFO. This can only be done if the pixelvalve is disabled though.
> > > >
> > > > In order to overcome this, we can configure the pixelvalve during
> > > > mode_set_no_fb, but only enable it in atomic_enable and flush the FIFO
> > > > there, and in atomic_disable disable the pixelvalve again.
> > >
> > > What displays has this been tested with?  Getting this sequencing
> > > right is so painful, and things like DSI are tricky to get to light
> > > up.
> >
> > That FIFO is between the HVS and the HDMI PVs, so this was obviously
> > tested against that. Dave also tested the DSI output IIRC, so we should
> > be covered here.
>
> DSI wasn't working on the first patch set that Maxime sent - I haven't
> tested this one as yet but will do so.
> DPI was working early on to both an Adafruit 800x480 DPI panel, and
> via a VGA666 as VGA.
> HDMI is obviously working.
> VEC is being ignored now. The clock structure is more restricted than
> earlier chips, so to get the required clocks for the VEC without using
> fractional divides it compromises the clock that other parts of the
> system can run at (IIRC including the ARM). That's why the VEC has to
> be explicitly enabled for the firmware to enable it as the only
> output. It's annoying, but that's just a restriction of the chip.

I'm more concerned with "make sure we don't regress pre-pi4 with this
series" than "pi4 displays all work from the beginning"