[PATCH] drm: bridge: dw-mipi-dsi: Drop panel_bridge post_disable call

[Jagan Teki]

On Tue, May 16, 2023 at 1:47 PM Marek Vasut <marex at denx.de> wrote:
>
> On 5/16/23 10:12, Jagan Teki wrote:
> > Hi Marek and Neil,
> >
> > On Sun, May 14, 2023 at 1:40 AM Marek Vasut <marex at denx.de> wrote:
> >>
> >> This panel_bridge post_disable callback is called from the bridge chain now,
> >> so drop the explicit call here. This fixes call imbalance, where this driver
> >> does not call ->pre_enable, but does call ->post_disable . In case either of
> >> the two callbacks implemented in one of the panel or bridge drivers contains
> >> any operation with refcounted object, like regulator, this would make kernel
> >> complain about the imbalance.
> >>
> >> This can be triggered e.g. with ST7701 driver, which operates on regulators
> >> in its prepare/unprepare callbacks, which are called from pre_enable/post_disable
> >> callbacks respectively. The former is called once, the later twice, during
> >> entry to suspend.
> >>
> >> Drop the post_disable call to fix the imbalance.
> >>
> >> Signed-off-by: Marek Vasut <marex at denx.de>
> >> ---
> >> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
> >> Cc: Antonio Borneo <antonio.borneo at foss.st.com>
> >> Cc: Daniel Vetter <daniel at ffwll.ch>
> >> Cc: David Airlie <airlied at gmail.com>
> >> Cc: Jernej Skrabec <jernej.skrabec at gmail.com>
> >> Cc: Jonas Karlman <jonas at kwiboo.se>
> >> Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
> >> Cc: Marek Vasut <marex at denx.de>
> >> Cc: Neil Armstrong <neil.armstrong at linaro.org>
> >> Cc: Philipp Zabel <p.zabel at pengutronix.de>
> >> Cc: Philippe Cornu <philippe.cornu at foss.st.com>
> >> Cc: Robert Foss <robert.foss at linaro.org>
> >> Cc: Vincent Abriou <vincent.abriou at st.com>
> >> Cc: Yannick Fertre <yannick.fertre at foss.st.com>
> >> Cc: dri-devel at lists.freedesktop.org
> >> ---
> >>   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 9 ---------
> >>   1 file changed, 9 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> >> index b2efecf7d1603..63ac972547361 100644
> >> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> >> @@ -859,15 +859,6 @@ static void dw_mipi_dsi_bridge_post_atomic_disable(struct drm_bridge *bridge,
> >>           */
> >>          dw_mipi_dsi_set_mode(dsi, 0);
> >>
> >> -       /*
> >> -        * TODO Only way found to call panel-bridge post_disable &
> >> -        * panel unprepare before the dsi "final" disable...
> >> -        * This needs to be fixed in the drm_bridge framework and the API
> >> -        * needs to be updated to manage our own call chains...
> >> -        */
> >> -       if (dsi->panel_bridge->funcs->post_disable)
> >> -               dsi->panel_bridge->funcs->post_disable(dsi->panel_bridge);
> >> -
> >
> > If my understanding was correct, the controller set the low-speed DCS
> > in pre_enable and high-speed DCS in enable. So I'm thinking this
> > explicit post_disable still needs to revert the operation within the
> > bridge chain. I didn't test this but trying to understand how the
> > existing behaviour is satisfied if we drop this.
>
> Did I miss a panel_bridge pre_enable call somewhere in the driver ?
> Where is it ?

Haa, sorry the next bridge pre_enable.  driver setting the
command-mode (low-speed) in mode_set so when the next bridge
pre_enable is called, low-speed DCS can be sent, then the bridge
enable() sets video mode (high-speed). This is where an explicit
post_disable would be required, this is what I understood so far.

Jagan.