Hi Gregory,
On 2014-08-29 12:43, Gregory CLEMENT wrote:
When the SSCG (Spread Spectrum Clock Generator) is enabled, it shifts
the frequency of the clock. The percentage is no more than 1% but when
the clock is used for a timer it leads to a clock drift.
Thank you so much for this series. I'm running 3.16 and without these
patches ntpd is all over the place, so it is a huge improvement I do
have a comment further down though..
This patch allows to correct the affected clock when the SSCG is
enabled. The check is done in an new optional function related to each
SoC: is_sscg_enabled(). If this function is not present then no
correction is done on the clock frequency.
Signed-off-by: Gregory CLEMENT <[email protected]>
---
drivers/clk/mvebu/common.c | 74
++++++++++++++++++++++++++++++++++++++++++++++
drivers/clk/mvebu/common.h | 1 +
2 files changed, 75 insertions(+)
diff --git a/drivers/clk/mvebu/common.c b/drivers/clk/mvebu/common.c
index 25ceccf939ad..834d36cf79b0 100644
--- a/drivers/clk/mvebu/common.c
+++ b/drivers/clk/mvebu/common.c
@@ -26,8 +26,78 @@
* Core Clocks
*/
+#define SSCG_CONF_MODE(reg) (((reg) >> 16) & 0x3)
+#define SSCG_SPREAD_DOWN 0x0
+#define SSCG_SPREAD_UP 0x1
+#define SSCG_SPREAD_CENTRAL 0x2
+#define SSCG_CONF_LOW(reg) (((reg) >> 8) & 0xFF)
+#define SSCG_CONF_HIGH(reg) ((reg) & 0xFF)
+
static struct clk_onecell_data clk_data;
+static u32 fix_sscg_deviation(struct device_node *np, u32 system_clk)
+{
+ struct device_node *sscg_np = NULL;
+ void __iomem *sscg_map;
+ u32 sscg_reg;
+ s32 low_bound, high_bound;
+ u64 freq_swing_half;
+
+ sscg_np = of_find_node_by_name(np, "sscg");
+ if (sscg_np == NULL) {
+ pr_err("cannot get SSCG register node\n");
+ return system_clk;
+ }
+
+ sscg_map = of_iomap(sscg_np, 0);
+ if (sscg_map == NULL) {
+ pr_err("cannot map SSCG register\n");
+ goto out;
+ }
+
+ sscg_reg = readl(sscg_map);
+ high_bound = SSCG_CONF_HIGH(sscg_reg);
+ low_bound = SSCG_CONF_LOW(sscg_reg);
+
+ if ((high_bound - low_bound) <= 0)
+ goto out;
+ /*
+ * From the datasheet we got the following formula
+ * Spread percentage = 1/96 * (H - L) / H
In the datasheet it says the percentage is 0.96 * (H - L) / H. 1/96 is
close but not the same as 0.0096.
+ * H = SSCG_High_Boundary
+ * L = SSCG_Low_Boundary
+ *
+ * As the deviation is half of spread then it lead to the
+ * following formula in the code.
+ *
+ * To avoid an overflow and not lose any significant digit in
+ * the same time we have to use a 64 bit integer.
+ */
+
+ freq_swing_half = (((u64)high_bound - (u64)low_bound)
+ * (u64)system_clk);
+ do_div(freq_swing_half, (2 * 96 * high_bound));
So this would be become :-
/* NB: 0.96% = 0.0048 or 3/625 */
freq_swing_half = (((u64)high_bound - (u64)low_bound)
* (u64)system_clk * 3);
do_div(freq_swing_half, (625 * high_bound));
+
+ switch (SSCG_CONF_MODE(sscg_reg)) {
+ case SSCG_SPREAD_DOWN:
+ system_clk -= freq_swing_half;
+ break;
+ case SSCG_SPREAD_UP:
+ system_clk += freq_swing_half;
+ break;
+ case SSCG_SPREAD_CENTRAL:
+ default:
+ break;
+ }
+
+ iounmap(sscg_map);
+
+out:
+ of_node_put(sscg_np);
+
+ return system_clk;
+}
+
void __init mvebu_coreclk_setup(struct device_node *np,
const struct coreclk_soc_desc *desc)
{
@@ -62,6 +132,10 @@ void __init mvebu_coreclk_setup(struct device_node
*np,
of_property_read_string_index(np, "clock-output-names", 1,
&cpuclk_name);
rate = desc->get_cpu_freq(base);
+
+ if (desc->is_sscg_enabled && desc->is_sscg_enabled(base))
+ rate = fix_sscg_deviation(np, rate);
+
clk_data.clks[1] = clk_register_fixed_rate(NULL, cpuclk_name, NULL,
CLK_IS_ROOT, rate);
WARN_ON(IS_ERR(clk_data.clks[1]));
diff --git a/drivers/clk/mvebu/common.h b/drivers/clk/mvebu/common.h
index f968b4d9df92..495f94ff4c90 100644
--- a/drivers/clk/mvebu/common.h
+++ b/drivers/clk/mvebu/common.h
@@ -28,6 +28,7 @@ struct coreclk_soc_desc {
u32 (*get_tclk_freq)(void __iomem *sar);
u32 (*get_cpu_freq)(void __iomem *sar);
void (*get_clk_ratio)(void __iomem *sar, int id, int *mult, int
*div);
+ bool (*is_sscg_enabled)(void __iomem *sar);
const struct coreclk_ratio *ratios;
int num_ratios;
};
I don't have a good way to measure the difference but my small
modification seems correct as per the datasheet.
Regards,
Leigh.
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