Make video port registers nonvolatile. As DSP_CTRL register is written
to twice due to gamma LUT enable bit which is set outside of the main
DSP_CTRL initialization within atomic_enable (for rk356x case it is also
necesarry to always disable gamma LUT before writing a new LUT) there is
a chance that DSP_CTRL value read-out in gamma LUT init/update code is
not the one which was written by the preceding DSP_CTRL initialization
code within atomic_enable. This might result in misconfigured DSP_CTRL
which leads to no visual output[1]. Since DSP_CTRL write takes effect
after VSYNC[1] the issue is not always present. When tested on Pinetab2
with kernel 6.14 it happenes only when DRM is compiled as a module[1].
In order to confirm that it is because of timing I inserted 18ms udelay
before vop2_crtc_atomic_try_set_gamma in atomic enable and compiled DRM
as module - this has also fixed the issue on Pinetab2.

[1] https://lore.kernel.org/linux-rockchip/562b38e5.a496.1975f09f983.Coremail.andyshrk@163.com/ (local)

Reported-by: Diederik de Haas <redacted>
Closes: https://lore.kernel.org/linux-rockchip/DAEVDSTMWI1E.J454VZN0R9MA@cknow.org/ (local)
Suggested-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Piotr Zalewski <redacted>
---
drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
index d0f5fea15e21..241060cc24cb 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c

@@ -2589,12 +2589,13 @@ static int vop2_win_init(struct vop2 *vop2)

}

/*
- * The window registers are only updated when config done is written.
- * Until that they read back the old value. As we read-modify-write
- * these registers mark them as non-volatile. This makes sure we read
- * the new values from the regmap register cache.
+ * The window and video port registers are only updated when config
+ * done is written. Until that they read back the old value. As we
+ * read-modify-write these registers mark them as non-volatile. This
+ * makes sure we read the new values from the regmap register cache.
 */
static const struct regmap_range vop2_nonvolatile_range[] = {
+	regmap_reg_range(RK3568_VP0_CTRL_BASE, RK3588_VP3_CTRL_BASE+255),