[PATCH v2] drm/bridge: tc358767: Enable FRMSYNC timing generator

[Dmitry Baryshkov]

On Tue, May 14, 2024 at 02:47:24AM +0200, Marek Vasut wrote:
> TC9595 datasheet Video Path0 Control (VPCTRL0) Register bit FRMSYNC description
> says "This bit should be disabled only in video mode transmission where Host
> transmits video timing together with video data and where pixel clock source
> is from DSI clock." . This driver always sources pixel clock from external xtal,
> therefore the FRMSYNC bit must always be enabled, enable it.
> 
> This fixes an actual issue with DSI-to-DPI mode, where the display would
> randomly show subtle pixel flickering, or wobble, or shimmering. This is
> visible on solid gray color, but the degree of the shimmering differs
> between boots, which makes it hard to debug.
> 
> There is a caveat to the FRMSYNC and this bridge pixel PLL, which can only
> generate pixel clock with limited accuracy, it may therefore be necessary
> to reduce the HFP to fit into line length of input pixel data, to avoid any
> possible overflows, which make the output video look striped horizontally.
> 
> Reviewed-by: Robert Foss <rfoss at kernel.org>
> Signed-off-by: Marek Vasut <marex at denx.de>
> ---
> Cc: Adam Ford <aford173 at gmail.com>
> Cc: Alexander Stein <alexander.stein at ew.tq-group.com>
> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: David Airlie <airlied at gmail.com>
> Cc: Frieder Schrempf <frieder.schrempf at kontron.de>
> Cc: Jernej Skrabec <jernej.skrabec at gmail.com>
> Cc: Jonas Karlman <jonas at kwiboo.se>
> Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Michael Walle <mwalle at kernel.org>
> Cc: Neil Armstrong <neil.armstrong at linaro.org>
> Cc: Robert Foss <rfoss at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: dri-devel at lists.freedesktop.org
> Cc: kernel at dh-electronics.com
> ---
> V2: - Use plain DIV_ROUND_UP() instead of custom local one
>     - Add RB from Robert
> ---
>  drivers/gpu/drm/bridge/tc358767.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>


-- 
With best wishes
Dmitry