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

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Message-ID: <CADaigPU7c=1u47R9GzvGCH_Z2fywY1foGYEy=KbBikjUQpwUFg@mail.gmail.com>
Date:   Wed, 27 May 2020 09:54:44 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v3 032/105] drm/vc4: crtc: Enable and disable the PV in
 atomic_enable / disable

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.