OMAP3630: Clock: Workaround for DPLL HS divider limitation

This patch implements a workaround for the DPLL HS divider limitation
in OMAP3630 as given by Errata ID: i556.

Errata:
When PWRDN bit is set, it resets the internal HSDIVIDER divide-by value (Mx).
The reset value gets loaded instead of the previous value.
The following HSDIVIDERs exhibit above behavior:
. DPLL4 : M6 / M5 / M4 / M3 / M2 (CM_CLKEN_PLL[31:26] register bits)
. DPLL3 : M3 (CM_CLKEN_PLL[12] register bit).

Work Around:
It is mandatory to apply the following sequence to ensure the write
value will
be loaded in DPLL HSDIVIDER FSM:
The global sequence when using PWRDN bit is the following:
. Disable Mx HSDIVIDER clock output related functional clock enable bits
        (in CM_FCLKEN_xxx / CM_ICLKEN_xxx)
. Enable PWRDN bit of HSDIVIDER
. Disable PWRDN bit of HSDIVIDER
. Read current HSDIVIDER register value
. Write different value in HSDIVIDER register
. Write expected value in HSDIVIDER register
. Enable Mx HSDIVIDER clock output related functional clocks
        (CM_FCLKEN_xxx / CM_ICLKEN_xxx)

Signed-off-by: Mike Turquette <mturquette@ti.com>
Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
Signed-off-by: Vijaykumar GN <vijaykumar.gn@ti.com>
[paul@pwsan.com: updated patch to apply; made workaround function static;
 marked as being 36xx-specific]
Signed-off-by: Paul Walmsley <paul@pwsan.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/arch/arm/mach-omap2/clock34xx.c b/arch/arm/mach-omap2/clock34xx.c
index de7391b6bcf..9039e8cbe48 100644
--- a/arch/arm/mach-omap2/clock34xx.c
+++ b/arch/arm/mach-omap2/clock34xx.c
@@ -150,6 +150,49 @@ const struct clkops clkops_omap3430es2_hsotgusb_wait = {
 	.find_companion = omap2_clk_dflt_find_companion,
 };
 
+/**
+ * omap36xx_pwrdn_clk_enable_with_hsdiv_restore - enable clocks suffering
+ *         from HSDivider PWRDN problem Implements Errata ID: i556.
+ * @clk: DPLL output struct clk
+ *
+ * 3630 only: dpll3_m3_ck, dpll4_m2_ck, dpll4_m3_ck, dpll4_m4_ck,
+ * dpll4_m5_ck & dpll4_m6_ck dividers gets loaded with reset
+ * valueafter their respective PWRDN bits are set.  Any dummy write
+ * (Any other value different from the Read value) to the
+ * corresponding CM_CLKSEL register will refresh the dividers.
+ */
+static int omap36xx_pwrdn_clk_enable_with_hsdiv_restore(struct clk *clk)
+{
+	u32 dummy_v, orig_v, clksel_shift;
+	int ret;
+
+	/* Clear PWRDN bit of HSDIVIDER */
+	ret = omap2_dflt_clk_enable(clk);
+
+	/* Restore the dividers */
+	if (!ret) {
+		clksel_shift = __ffs(clk->parent->clksel_mask);
+		orig_v = __raw_readl(clk->parent->clksel_reg);
+		dummy_v = orig_v;
+
+		/* Write any other value different from the Read value */
+		dummy_v ^= (1 << clksel_shift);
+		__raw_writel(dummy_v, clk->parent->clksel_reg);
+
+		/* Write the original divider */
+		__raw_writel(orig_v, clk->parent->clksel_reg);
+	}
+
+	return ret;
+}
+
+const struct clkops clkops_omap36xx_pwrdn_with_hsdiv_wait_restore = {
+	.enable		= omap36xx_pwrdn_clk_enable_with_hsdiv_restore,
+	.disable	= omap2_dflt_clk_disable,
+	.find_companion	= omap2_clk_dflt_find_companion,
+	.find_idlest	= omap2_clk_dflt_find_idlest,
+};
+
 const struct clkops omap3_clkops_noncore_dpll_ops = {
 	.enable		= omap3_noncore_dpll_enable,
 	.disable	= omap3_noncore_dpll_disable,