linux-kernel - Re: [PATCH v3 032/105] drm/vc4: crtc: Enable and disable the PV in atomic

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Date:   Wed, 3 Jun 2020 15:14:34 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Eric Anholt <eric@...olt.net>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        bcm-kernel-feedback-list@...adcom.com,
        Phil Elwell <phil@...pberrypi.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 032/105] drm/vc4: crtc: Enable and disable the PV in
 atomic_enable / disable

Hi Stefan,

On Tue, Jun 02, 2020 at 10:03:13PM +0200, Stefan Wahren wrote:
> Am 02.06.20 um 21:31 schrieb Eric Anholt:
> > On Tue, Jun 2, 2020 at 8:02 AM Dave Stevenson
> > <dave.stevenson@...pberrypi.com> wrote:
> >> Hi Maxime and Eric
> >>
> >> On Tue, 2 Jun 2020 at 15:12, Maxime Ripard <maxime@...no.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@...no.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"
> 
> unfortuntely i can confirm this. With this patch series (using Maxime's
> git repo with multi_v7_defconfig) my Raspberry Pi 3 B hangs up while
> starting X (screen stays black, heartbeat stops, no more output at the
> debug UART). AFAIR v2 didn't had this issue.

Did it happen with a DSI display or something else?

I've been trying to setup the DSI display on an RPi3 today, but noticed
that it looks like there's a regression in next that prevents the HDMI
driver to load entirely (without my patches).

Maxime

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