commit da8892d4 upstream.

The adv7604 driver platform data contains fields for configuring the drive
strength of the output pins. When probing the driver through DT these
fields are not explicitly initialized, which means they are left at 0. This
is a reserved setting for the drive strength configuration though and can
cause signal integrity issues.

Whether these signal integrity issues are visible depends on the PCB
specifics (e.g. the higher the load capacitance for the output the more
visible the issue). But it has been observed on existing solutions at high
pixel clock rates.

Initialize the drive strength settings to the power-on-reset value of the
device when probing through devicetree to avoid this issue.

Fixes: 0e158be0162b ("adv7604: Add DT support")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>