drm/rockchip: vop2: Avoid use regmap_reinit_cache at runtime

Marek Report a possible irq lock inversion dependency warning when
commit 81a06f1 ("Revert "drm/rockchip: vop2: Use regcache_sync()
to fix suspend/resume"") lands linux-next.

I can reproduce this warning with:
CONFIG_PROVE_LOCKING=y
CONFIG_DEBUG_LOCKDEP=y

It seems than when use regmap_reinit_cache at runtime whith Mark's
commit 3d59c22 ("drm/rockchip: vop2: Convert to use maple tree
register cache"), it will trigger a possible irq lock inversion dependency
warning.

One solution is switch back to REGCACHE_RBTREE, but it seems that
REGCACHE_MAPLE is the future, so I avoid using regmap_reinit_cache,
and drop all the regcache when vop is disabled, then we get a fresh
start at next enbable time.

Fixes: 81a06f1 ("Revert "drm/rockchip: vop2: Use regcache_sync() to fix suspend/resume"")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Closes: https://lore.kernel.org/all/98a9f15d-30ac-47bf-9b93-3aa2c9900f7b@samsung.com/
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
[dropped the large kernel log of the lockdep report from the message]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231217084415.2373043-1-andyshrk@163.com

Author: Andy Yan

drivers/gpu/drm/rockchip/rockchip_drm_vop2.c

@@ -959,12 +959,6 @@ static void vop2_enable(struct vop2 *vop2)
 		return;
 	}
 
-	ret = regmap_reinit_cache(vop2->map, &vop2_regmap_config);
-	if (ret) {
-		drm_err(vop2->drm, "failed to reinit cache: %d\n", ret);
-		return;
-	}
-
 	if (vop2->data->soc_id == 3566)
 		vop2_writel(vop2, RK3568_OTP_WIN_EN, 1);
 
@@ -996,6 +990,8 @@ static void vop2_disable(struct vop2 *vop2)
 
 	pm_runtime_put_sync(vop2->dev);
 
+	regcache_drop_region(vop2->map, 0, vop2_regmap_config.max_register);
+
 	clk_disable_unprepare(vop2->pclk);
 	clk_disable_unprepare(vop2->aclk);
 	clk_disable_unprepare(vop2->hclk);