clk: ti: omap36xx: Work around sprz319 advisory 2.1

The OMAP36xx DPLL5, driving EHCI USB, can be subject to a long-term
frequency drift. The frequency drift magnitude depends on the VCO update
rate, which is inversely proportional to the PLL divider. The kernel
DPLL configuration code results in a high value for the divider, leading
to a long term drift high enough to cause USB transmission errors. In
the worst case the USB PHY's ULPI interface can stop responding,
breaking USB operation completely. This manifests itself on the
Beagleboard xM by the LAN9514 reporting 'Cannot enable port 2. Maybe the
cable is bad?' in the kernel log.

Errata sprz319 advisory 2.1 documents PLL values that minimize the
drift. Use them automatically when DPLL5 is used for USB operation,
which we detect based on the requested clock rate. The clock framework
will still compute the PLL parameters and resulting rate as usual, but
the PLL M and N values will then be overridden. This can result in the
effective clock rate being slightly different than the rate cached by
the clock framework, but won't cause any adverse effect to USB
operation.

Signed-off-by: Richard Watts <rrw@kynesim.co.uk>
[Upported from v3.2 to v4.9]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/drivers/clk/ti/dpll3xxx.c b/drivers/clk/ti/dpll3xxx.c
index 88f2ce81ba55..4cdd28a25584 100644
--- a/drivers/clk/ti/dpll3xxx.c
+++ b/drivers/clk/ti/dpll3xxx.c
@@ -838,3 +838,70 @@ int omap3_dpll4_set_rate_and_parent(struct clk_hw *hw, unsigned long rate,
 	return omap3_noncore_dpll_set_rate_and_parent(hw, rate, parent_rate,
 						      index);
 }
+
+/* Apply DM3730 errata sprz319 advisory 2.1. */
+static bool omap3_dpll5_apply_errata(struct clk_hw *hw,
+				     unsigned long parent_rate)
+{
+	struct omap3_dpll5_settings {
+		unsigned int rate, m, n;
+	};
+
+	static const struct omap3_dpll5_settings precomputed[] = {
+		/*
+		 * From DM3730 errata advisory 2.1, table 35 and 36.
+		 * The N value is increased by 1 compared to the tables as the
+		 * errata lists register values while last_rounded_field is the
+		 * real divider value.
+		 */
+		{ 12000000,  80,  0 + 1 },
+		{ 13000000, 443,  5 + 1 },
+		{ 19200000,  50,  0 + 1 },
+		{ 26000000, 443, 11 + 1 },
+		{ 38400000,  25,  0 + 1 }
+	};
+
+	const struct omap3_dpll5_settings *d;
+	struct clk_hw_omap *clk = to_clk_hw_omap(hw);
+	struct dpll_data *dd;
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(precomputed); ++i) {
+		if (parent_rate == precomputed[i].rate)
+			break;
+	}
+
+	if (i == ARRAY_SIZE(precomputed))
+		return false;
+
+	d = &precomputed[i];
+
+	/* Update the M, N and rounded rate values and program the DPLL. */
+	dd = clk->dpll_data;
+	dd->last_rounded_m = d->m;
+	dd->last_rounded_n = d->n;
+	dd->last_rounded_rate = div_u64((u64)parent_rate * d->m, d->n);
+	omap3_noncore_dpll_program(clk, 0);
+
+	return true;
+}
+
+/**
+ * omap3_dpll5_set_rate - set rate for omap3 dpll5
+ * @hw: clock to change
+ * @rate: target rate for clock
+ * @parent_rate: rate of the parent clock
+ *
+ * Set rate for the DPLL5 clock. Apply the sprz319 advisory 2.1 on OMAP36xx if
+ * the DPLL is used for USB host (detected through the requested rate).
+ */
+int omap3_dpll5_set_rate(struct clk_hw *hw, unsigned long rate,
+			 unsigned long parent_rate)
+{
+	if (rate == OMAP3_DPLL5_FREQ_FOR_USBHOST * 8) {
+		if (omap3_dpll5_apply_errata(hw, parent_rate))
+			return 0;
+	}
+
+	return omap3_noncore_dpll_set_rate(hw, rate, parent_rate);
+}