1 files changed, 40 insertions, 0 deletions

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
index 9e1224d54729..b535621f4f78 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
@@ -107,6 +107,14 @@ static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb)
 		clk_prepare_enable(mxsfb->clk_disp_axi);
 	clk_prepare_enable(mxsfb->clk);
 
+	/* Increase number of outstanding requests on all supported IPs */
+	if (mxsfb->devdata->has_ctrl2) {
+		reg = readl(mxsfb->base + LCDC_V4_CTRL2);
+		reg &= ~CTRL2_SET_OUTSTANDING_REQS_MASK;
+		reg |= CTRL2_SET_OUTSTANDING_REQS_16;
+		writel(reg, mxsfb->base + LCDC_V4_CTRL2);
+	}
+
 	/* If it was disabled, re-enable the mode again */
 	writel(CTRL_DOTCLK_MODE, mxsfb->base + LCDC_CTRL + REG_SET);
 
@@ -115,6 +123,35 @@ static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb)
 	reg |= VDCTRL4_SYNC_SIGNALS_ON;
 	writel(reg, mxsfb->base + LCDC_VDCTRL4);
 
+	/*
+	 * Enable recovery on underflow.
+	 *
+	 * There is some sort of corner case behavior of the controller,
+	 * which could rarely be triggered at least on i.MX6SX connected
+	 * to 800x480 DPI panel and i.MX8MM connected to DPI->DSI->LVDS
+	 * bridged 1920x1080 panel (and likely on other setups too), where
+	 * the image on the panel shifts to the right and wraps around.
+	 * This happens either when the controller is enabled on boot or
+	 * even later during run time. The condition does not correct
+	 * itself automatically, i.e. the display image remains shifted.
+	 *
+	 * It seems this problem is known and is due to sporadic underflows
+	 * of the LCDIF FIFO. While the LCDIF IP does have underflow/overflow
+	 * IRQs, neither of the IRQs trigger and neither IRQ status bit is
+	 * asserted when this condition occurs.
+	 *
+	 * All known revisions of the LCDIF IP have CTRL1 RECOVER_ON_UNDERFLOW
+	 * bit, which is described in the reference manual since i.MX23 as
+	 * "
+	 *   Set this bit to enable the LCDIF block to recover in the next
+	 *   field/frame if there was an underflow in the current field/frame.
+	 * "
+	 * Enable this bit to mitigate the sporadic underflows.
+	 */
+	reg = readl(mxsfb->base + LCDC_CTRL1);
+	reg |= CTRL1_RECOVER_ON_UNDERFLOW;
+	writel(reg, mxsfb->base + LCDC_CTRL1);
+
 	writel(CTRL_RUN, mxsfb->base + LCDC_CTRL + REG_SET);
 }
 
@@ -206,6 +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);