[PATCH] drm: mxsfb_crtc: Reset the eLCDIF controller

[Fabio Estevam]

According to the eLCDIF initialization steps listed in the MX6SX
Reference Manual the eLCDIF block reset is mandatory. 

Without performing the eLCDIF reset the display shows garbage content
when the kernel boots.

In earlier tests this issue has not been observed because the bootloader
was previously showing a splash screen and the bootloader display driver
does properly implement the eLCDIF reset.

Add the eLCDIF reset to the driver, so that it can operate correctly
independently of the bootloader.

Tested on a imx6sx-sdb board.

Cc: <stable at vger.kernel.org>
Signed-off-by: Fabio Estevam <fabio.estevam at nxp.com>
---
 drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 53 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
index 1144e0c..47e0941 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -35,6 +35,13 @@
 #include "mxsfb_drv.h"
 #include "mxsfb_regs.h"
 
+#define MXS_SET_ADDR		0x4
+#define MXS_CLR_ADDR		0x8
+#define MODULE_CLKGATE		BIT(30)
+#define MODULE_SFTRST		BIT(31)
+/* 1 second delay should be plenty of time for block reset. */
+#define RESET_MAX_TIMEOUT	1000000
+
 static u32 set_hsync_pulse_width(struct mxsfb_drm_private *mxsfb, u32 val)
 {
 	return (val & mxsfb->devdata->hs_wdth_mask) <<
@@ -159,6 +166,48 @@ static void mxsfb_disable_controller(struct mxsfb_drm_private *mxsfb)
 		clk_disable_unprepare(mxsfb->clk_disp_axi);
 }
 
+/*
+ * Clear the bit and poll it cleared.  This is usually called with
+ * a reset address and mask being either SFTRST(bit 31) or CLKGATE
+ * (bit 30).
+ */
+static int clear_poll_bit(void __iomem *addr, u32 mask)
+{
+	unsigned int timeout = RESET_MAX_TIMEOUT;
+
+	/* clear the bit */
+	writel(mask, addr + MXS_CLR_ADDR);
+
+	udelay(1);
+
+	/* poll the bit becoming clear */
+	while ((readl(addr) & mask) && --timeout)
+		;
+
+	return !timeout;
+}
+
+static int mxsfb_reset_block(void __iomem *reset_addr)
+{
+	int ret;
+
+	/* clear and poll SFTRST */
+	ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
+	if (ret)
+		return ret;
+
+	/* clear CLKGATE */
+	writel(MODULE_CLKGATE, reset_addr + MXS_CLR_ADDR);
+
+	/* clear and poll SFTRST */
+	ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
+	if (ret)
+		return ret;
+
+	/* clear and poll CLKGATE */
+	return clear_poll_bit(reset_addr, MODULE_CLKGATE);
+}
+
 static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 {
 	struct drm_display_mode *m = &mxsfb->pipe.crtc.state->adjusted_mode;
@@ -173,6 +222,10 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 	 */
 	mxsfb_enable_axi_clk(mxsfb);
 
+	err = mxsfb_reset_block(mxsfb->base);
+	if (err)
+		return;
+
 	/* Clear the FIFOs */
 	writel(CTRL1_FIFO_CLEAR, mxsfb->base + LCDC_CTRL1 + REG_SET);
 
-- 
2.7.4