[PATCH v2 4/5] clk: imx6: Fix procedure to switch the parent of LDB_DI_CLK

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

From: Fabio Estevam <fabio.estevam@nxp.com>

Due to incorrect placement of the clock gate cell in the ldb_di[x]_clk
tree, the glitchy parent mux of ldb_di[x]_clk can cause a glitch to
enter the ldb_di_ipu_div divider. If the divider gets locked up, no
ldb_di[x]_clk is generated, and the LVDS display will hang when the
ipu_di_clk is sourced from ldb_di_clk.

To fix the problem, both the new and current parent of the ldb_di_clk
should be disabled before the switch. This patch ensures that correct
steps are followed when ldb_di_clk parent is switched in the beginning
of boot. The glitchy muxes are then registered as read-only. The clock
parent can be selected using the assigned-clocks and
assigned-clock-parents properties of the ccm device tree node:

        &clks {
                assigned-clocks = <&clks IMX6QDL_CLK_LDB_DI0_SEL>,
                                  <&clks IMX6QDL_CLK_LDB_DI1_SEL>;
                assigned-clock-parents = <&clks IMX6QDL_CLK_MMDC_CH1_AXI>,
                                         <&clks IMX6QDL_CLK_PLL5_VIDEO_DIV>;
        };

The issue is explained in detail in EB821 ("LDB Clock Switch Procedure &
i.MX6 Asynchronous Clock Switching Guidelines") [1].

[1] http://www.nxp.com/files/32bit/doc/eng_bulletin/EB821.pdf

Signed-off-by: Ranjani Vaidyanathan <Ranjani.Vaidyanathan@nxp.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Akshay Bhat <akshay.bhat@timesys.com>
Tested-by Joshua Clayton <stillcompiling@gmail.com>
Tested-by: Charles Kang <Charles.Kang@advantech.com.tw>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
[afa: ported to barebox from Linux commit 5d283b0838]
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 drivers/clk/imx/clk-imx6.c | 264 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 261 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/imx/clk-imx6.c b/drivers/clk/imx/clk-imx6.c
index 22f33aee03e9..69586f04a21f 100644
--- a/drivers/clk/imx/clk-imx6.c
+++ b/drivers/clk/imx/clk-imx6.c
@@ -64,6 +64,12 @@ static inline int cpu_is_plus(void)
 	return cpu_is_mx6qp() || cpu_is_mx6dp();
 }
 
+/* Audio/Video PLL post dividers don't work on i.MX6q revision 1.0 */
+static inline int cpu_has_working_video_pll_post_div(void) {
+	return !((cpu_is_mx6q() || cpu_is_mx6d()) &&
+		 imx_silicon_revision() == IMX_CHIP_REV_1_0);
+}
+
 /* i.MX6 Quad/Dual/DualLite/Solo are all affected */
 static inline int cpu_has_err009219(void) {
 	return cpu_is_mx6d() || cpu_is_mx6q() ||
@@ -299,9 +305,89 @@ static struct clk_div_table video_div_table[] = {
 	{ /* sentinel */ }
 };
 
+static int ldb_di_sel_by_clock_id(int clock_id)
+{
+	switch (clock_id) {
+	case IMX6QDL_CLK_PLL5_VIDEO_DIV:
+		if (!cpu_has_working_video_pll_post_div())
+			return -ENOENT;
+		return 0;
+	case IMX6QDL_CLK_PLL2_PFD0_352M:
+		return 1;
+	case IMX6QDL_CLK_PLL2_PFD2_396M:
+		return 2;
+	case IMX6QDL_CLK_MMDC_CH1_AXI:
+		return 3;
+	case IMX6QDL_CLK_PLL3_USB_OTG:
+		return 4;
+	default:
+		return -ENOENT;
+	}
+}
+
+static void of_assigned_ldb_sels(struct device_node *node,
+				 unsigned int *ldb_di0_sel,
+				 unsigned int *ldb_di1_sel)
+{
+	struct of_phandle_args clkspec;
+	int index, rc, num_parents;
+	int parent, child, sel;
+
+	num_parents = of_count_phandle_with_args(node, "assigned-clock-parents",
+						 "#clock-cells");
+	for (index = 0; index < num_parents; index++) {
+		rc = of_parse_phandle_with_args(node, "assigned-clock-parents",
+					"#clock-cells", index, &clkspec);
+		if (rc < 0) {
+			/* skip empty (null) phandles */
+			if (rc == -ENOENT)
+				continue;
+			else
+				return;
+		}
+		if (clkspec.np != node || clkspec.args[0] >= IMX6QDL_CLK_END) {
+			pr_err("ccm: parent clock %d not in ccm\n", index);
+			return;
+		}
+		parent = clkspec.args[0];
+
+		rc = of_parse_phandle_with_args(node, "assigned-clocks",
+				"#clock-cells", index, &clkspec);
+		if (rc < 0)
+			return;
+		if (clkspec.np != node || clkspec.args[0] >= IMX6QDL_CLK_END) {
+			pr_err("ccm: child clock %d not in ccm\n", index);
+			return;
+		}
+		child = clkspec.args[0];
+
+		if (child != IMX6QDL_CLK_LDB_DI0_SEL &&
+		    child != IMX6QDL_CLK_LDB_DI1_SEL)
+			continue;
+
+		sel = ldb_di_sel_by_clock_id(parent);
+		if (sel < 0) {
+			pr_err("ccm: invalid ldb_di%d parent clock: %d\n",
+			       child == IMX6QDL_CLK_LDB_DI1_SEL, parent);
+			continue;
+		}
+
+		if (child == IMX6QDL_CLK_LDB_DI0_SEL)
+			*ldb_di0_sel = sel;
+		if (child == IMX6QDL_CLK_LDB_DI1_SEL)
+			*ldb_di1_sel = sel;
+	}
+}
+
 #define CCM_CCDR		0x04
+#define CCM_CCSR		0x0c
+#define CCM_CS2CDR		0x2c
+
+#define CCDR_MMDC_CH1_MASK		BIT(16)
+#define CCSR_PLL3_SW_CLK_SEL		BIT(0)
 
-#define CCDR_MMDC_CH1_MASK	BIT(16)
+#define CS2CDR_LDB_DI0_CLK_SEL_SHIFT	9
+#define CS2CDR_LDB_DI1_CLK_SEL_SHIFT	12
 
 static void __init imx6q_mmdc_ch1_mask_handshake(void __iomem *ccm_base)
 {
@@ -312,7 +398,170 @@ static void __init imx6q_mmdc_ch1_mask_handshake(void __iomem *ccm_base)
 	writel(reg, ccm_base + CCM_CCDR);
 }
 
-static void imx6_add_video_clks(void __iomem *anab, void __iomem *cb)
+/*
+ * The only way to disable the MMDC_CH1 clock is to move it to pll3_sw_clk
+ * via periph2_clk2_sel and then to disable pll3_sw_clk by selecting the
+ * bypass clock source, since there is no CG bit for mmdc_ch1.
+ */
+static void mmdc_ch1_disable(void __iomem *ccm_base)
+{
+	unsigned int reg;
+
+	clk_set_parent(clks[IMX6QDL_CLK_PERIPH2_CLK2_SEL],
+		       clks[IMX6QDL_CLK_PLL3_USB_OTG]);
+
+	/*
+	 * Handshake with mmdc_ch1 module must be masked when changing
+	 * periph2_clk_sel.
+	 */
+	clk_set_parent(clks[IMX6QDL_CLK_PERIPH2], clks[IMX6QDL_CLK_PERIPH2_CLK2]);
+
+	/* Disable pll3_sw_clk by selecting the bypass clock source */
+	reg = readl(ccm_base + CCM_CCSR);
+	reg |= CCSR_PLL3_SW_CLK_SEL;
+	writel(reg, ccm_base + CCM_CCSR);
+}
+
+static void mmdc_ch1_reenable(void __iomem *ccm_base)
+{
+	unsigned int reg;
+
+	/* Enable pll3_sw_clk by disabling the bypass */
+	reg = readl(ccm_base + CCM_CCSR);
+	reg &= ~CCSR_PLL3_SW_CLK_SEL;
+	writel(reg, ccm_base + CCM_CCSR);
+
+	clk_set_parent(clks[IMX6QDL_CLK_PERIPH2], clks[IMX6QDL_CLK_PERIPH2_PRE]);
+}
+
+/*
+ * We have to follow a strict procedure when changing the LDB clock source,
+ * otherwise we risk introducing a glitch that can lock up the LDB divider.
+ * Things to keep in mind:
+ *
+ * 1. The current and new parent clock inputs to the mux must be disabled.
+ * 2. The default clock input for ldb_di0/1_clk_sel is mmdc_ch1_axi, which
+ *    has no CG bit.
+ * 3. pll2_pfd2_396m can not be gated if it is used as memory clock.
+ * 4. In the RTL implementation of the LDB_DI_CLK_SEL muxes the top four
+ *    options are in one mux and the PLL3 option along with three unused
+ *    inputs is in a second mux. There is a third mux with two inputs used
+ *    to decide between the first and second 4-port mux:
+ *
+ *    pll5_video_div 0 --|\
+ *    pll2_pfd0_352m 1 --| |_
+ *    pll2_pfd2_396m 2 --| | `-|\
+ *    mmdc_ch1_axi   3 --|/    | |
+ *                             | |--
+ *    pll3_usb_otg   4 --|\    | |
+ *                   5 --| |_,-|/
+ *                   6 --| |
+ *                   7 --|/
+ *
+ * The ldb_di0/1_clk_sel[1:0] bits control both 4-port muxes at the same time.
+ * The ldb_di0/1_clk_sel[2] bit controls the 2-port mux. The code below
+ * switches the parent to the bottom mux first and then manipulates the top
+ * mux to ensure that no glitch will enter the divider.
+ */
+static void init_ldb_clks(struct device_node *np, void __iomem *ccm_base)
+{
+	unsigned int reg;
+	unsigned int sel[2][4];
+	int i;
+
+	reg = readl(ccm_base + CCM_CS2CDR);
+	sel[0][0] = (reg >> CS2CDR_LDB_DI0_CLK_SEL_SHIFT) & 7;
+	sel[1][0] = (reg >> CS2CDR_LDB_DI1_CLK_SEL_SHIFT) & 7;
+
+	sel[0][3] = sel[0][2] = sel[0][1] = sel[0][0];
+	sel[1][3] = sel[1][2] = sel[1][1] = sel[1][0];
+
+	of_assigned_ldb_sels(np, &sel[0][3], &sel[1][3]);
+
+	for (i = 0; i < 2; i++) {
+		/* Warn if a glitch might have been introduced already */
+		if (sel[i][0] != 3) {
+			pr_warn("ccm: ldb_di%d_sel already changed from reset value: %d\n",
+				i, sel[i][0]);
+		}
+
+		if (sel[i][0] == sel[i][3])
+			continue;
+
+		/* Only switch to or from pll2_pfd2_396m if it is disabled */
+		if ((sel[i][0] == 2 || sel[i][3] == 2) &&
+		    (clk_get_parent(clks[IMX6QDL_CLK_PERIPH_PRE]) ==
+		     clks[IMX6QDL_CLK_PLL2_PFD2_396M])) {
+			pr_err("ccm: ldb_di%d_sel: couldn't disable pll2_pfd2_396m\n",
+			       i);
+			sel[i][3] = sel[i][2] = sel[i][1] = sel[i][0];
+			continue;
+		}
+
+		/* First switch to the bottom mux */
+		sel[i][1] = sel[i][0] | 4;
+
+		/* Then configure the top mux before switching back to it */
+		sel[i][2] = sel[i][3] | 4;
+
+		pr_debug("ccm: switching ldb_di%d_sel: %d->%d->%d->%d\n", i,
+			 sel[i][0], sel[i][1], sel[i][2], sel[i][3]);
+	}
+
+	if (sel[0][0] == sel[0][3] && sel[1][0] == sel[1][3])
+		return;
+
+	mmdc_ch1_disable(ccm_base);
+
+	for (i = 1; i < 4; i++) {
+		reg = readl(ccm_base + CCM_CS2CDR);
+		reg &= ~((7 << CS2CDR_LDB_DI0_CLK_SEL_SHIFT) |
+			 (7 << CS2CDR_LDB_DI1_CLK_SEL_SHIFT));
+		reg |= ((sel[0][i] << CS2CDR_LDB_DI0_CLK_SEL_SHIFT) |
+			(sel[1][i] << CS2CDR_LDB_DI1_CLK_SEL_SHIFT));
+		writel(reg, ccm_base + CCM_CS2CDR);
+	}
+
+	mmdc_ch1_reenable(ccm_base);
+}
+
+#define CCM_ANALOG_PLL_VIDEO	0xa0
+#define CCM_ANALOG_PFD_480	0xf0
+#define CCM_ANALOG_PFD_528	0x100
+
+#define PLL_ENABLE		BIT(13)
+
+#define PFD0_CLKGATE		BIT(7)
+#define PFD1_CLKGATE		BIT(15)
+#define PFD2_CLKGATE		BIT(23)
+#define PFD3_CLKGATE		BIT(31)
+
+static void disable_anatop_clocks(void __iomem *anatop_base)
+{
+	unsigned int reg;
+
+	/* Make sure PLL2 PFDs 0-2 are gated */
+	reg = readl(anatop_base + CCM_ANALOG_PFD_528);
+	/* Cannot gate PFD2 if pll2_pfd2_396m is the parent of MMDC clock */
+	if (clk_get_parent(clks[IMX6QDL_CLK_PERIPH_PRE]) ==
+	    clks[IMX6QDL_CLK_PLL2_PFD2_396M])
+		reg |= PFD0_CLKGATE | PFD1_CLKGATE;
+	else
+		reg |= PFD0_CLKGATE | PFD1_CLKGATE | PFD2_CLKGATE;
+	writel(reg, anatop_base + CCM_ANALOG_PFD_528);
+
+	/* Make sure PLL3 PFDs 0-3 are gated */
+	reg = readl(anatop_base + CCM_ANALOG_PFD_480);
+	reg |= PFD0_CLKGATE | PFD1_CLKGATE | PFD2_CLKGATE | PFD3_CLKGATE;
+	writel(reg, anatop_base + CCM_ANALOG_PFD_480);
+
+	/* Make sure PLL5 is disabled */
+	reg = readl(anatop_base + CCM_ANALOG_PLL_VIDEO);
+	reg &= ~PLL_ENABLE;
+	writel(reg, anatop_base + CCM_ANALOG_PLL_VIDEO);
+}
+
+static void imx6_add_video_clks(void __iomem *anab, void __iomem *cb, struct device_node *ccm_np)
 {
 	clks[IMX6QDL_CLK_PLL5_POST_DIV] = imx_clk_divider_table("pll5_post_div", "pll5_video", anab + 0xa0, 19, 2, post_div_table);
 	clks[IMX6QDL_CLK_PLL5_VIDEO_DIV] = imx_clk_divider_table("pll5_video_div", "pll5_post_div", anab + 0x170, 30, 2, video_div_table);
@@ -320,9 +569,18 @@ static void imx6_add_video_clks(void __iomem *anab, void __iomem *cb)
 	clks[IMX6QDL_CLK_IPU1_SEL]         = imx_clk_mux("ipu1_sel",         cb + 0x3c, 9,  2, ipu_sels,          ARRAY_SIZE(ipu_sels));
 	clks[IMX6QDL_CLK_IPU2_SEL]         = imx_clk_mux("ipu2_sel",         cb + 0x3c, 14, 2, ipu_sels,          ARRAY_SIZE(ipu_sels));
 
+	disable_anatop_clocks(anab);
+
 	imx6q_mmdc_ch1_mask_handshake(cb);
 
 	if (cpu_has_err009219()) {
+		/*
+		 * The LDB_DI0/1_SEL muxes should be read-only due to a hardware
+		 * bug. Set the muxes to the requested values before registering the
+		 * ldb_di_sel clocks.
+		 */
+		init_ldb_clks(ccm_np, cb);
+
 		clks[IMX6QDL_CLK_LDB_DI0_SEL] = imx_clk_mux_ldb("ldb_di0_sel",    cb + 0x2c, 9,  3, ldb_di_sels,      ARRAY_SIZE(ldb_di_sels));
 		clks[IMX6QDL_CLK_LDB_DI1_SEL] = imx_clk_mux_ldb("ldb_di1_sel",    cb + 0x2c, 12, 3, ldb_di_sels,       ARRAY_SIZE(ldb_di_sels));
 	} else {
@@ -527,7 +785,7 @@ static int imx6_ccm_probe(struct device_d *dev)
 	clkdev_add_physbase(clks[IMX6QDL_CLK_IPG], MX6_OCOTP_BASE_ADDR, NULL);
 
 	if (IS_ENABLED(CONFIG_DRIVER_VIDEO_IMX_IPUV3))
-		imx6_add_video_clks(anatop_base, ccm_base);
+		imx6_add_video_clks(anatop_base, ccm_base, dev->device_node);
 
 	writel(0xffffffff, ccm_base + CCGR0);
 	writel(0xf0ffffff, ccm_base + CCGR1); /* gate GPU3D, GPU2D */
-- 
2.20.1


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