[PATCH 5.13 130/300] drm: mxsfb: Clear FIFO_CLEAR bit

[Greg Kroah-Hartman]

From: Marek Vasut <marex@xxxxxxx>

[ Upstream commit 5e23c98178eb1a2cdb7c4fee9a39baf8cabf282d ]

Make sure the FIFO_CLEAR bit is latched in when configuring the
controller, so that the FIFO is really cleared. And then clear
the FIFO_CLEAR bit, since it is not self-clearing.

Fixes: 45d59d704080 ("drm: Add new driver for MXSFB controller")
Signed-off-by: Marek Vasut <marex@xxxxxxx>
Cc: Daniel Abrecht <public@xxxxxxxxxxxxxxxx>
Cc: Emil Velikov <emil.l.velikov@xxxxxxxxx>
Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Cc: Stefan Agner <stefan@xxxxxxxx>
Reviewed-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
Tested-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx> # i.Core MX8MM
Acked-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210620224946.189524-1-marex@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/gpu/drm/mxsfb/mxsfb_kms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
index 5bcc06c1ac0b..54f905ac75c0 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
@@ -243,6 +243,9 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 
 	/* Clear the FIFOs */
 	writel(CTRL1_FIFO_CLEAR, mxsfb->base + LCDC_CTRL1 + REG_SET);
+	readl(mxsfb->base + LCDC_CTRL1);
+	writel(CTRL1_FIFO_CLEAR, mxsfb->base + LCDC_CTRL1 + REG_CLR);
+	readl(mxsfb->base + LCDC_CTRL1);
 
 	if (mxsfb->devdata->has_overlay)
 		writel(0, mxsfb->base + LCDC_AS_CTRL);
-- 
2.30.2