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From:   Dave Stevenson <dave.stevenson@raspberrypi.com>
Date:   Tue, 2 Jun 2020 16:02:28 +0100
Message-ID: <CAPY8ntDZWJeu14mL5a0jqUWHFOEWm2OOBBkh4yjjP0oLU83UCQ@mail.gmail.com>
Subject: Re: [PATCH v3 032/105] drm/vc4: crtc: Enable and disable the PV in
 atomic_enable / disable
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     Eric Anholt <eric@anholt.net>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-rpi-kernel@lists.infradead.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>,
        Tim Gover <tim.gover@raspberrypi.com>,
        Phil Elwell <phil@raspberrypi.com>
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Hi Maxime and Eric

On Tue, 2 Jun 2020 at 15:12, Maxime Ripard <maxime@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@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.

  Dave