From: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
Allow to define a minimum fractional divider to use
in the devicetree.
This is primarily used to reduce clock-jitter introduced
by the fractional/MASH divider.
Signed-off-by: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
---
drivers/clk/bcm/clk-bcm2835.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index e5313ba..7048ca5 100644
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -711,6 +711,8 @@ struct bcm2835_clock_data {
u32 int_bits;
/* Number of fractional bits in the divider */
u32 frac_bits;
+ /* the minimum divider to allow when fractional */
+ u32 min_frac_div;
/* the mash value to use - see CM_MASH */
enum bcm2835_clock_mash_type mash;
bool mash_forced;
@@ -1709,13 +1711,21 @@ static int bcm2835_clock_determine_closest_rate(struct clk_hw *hw,
struct bcm2835_rates *rates,
size_t rate_cnt)
{
+ struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
+ const struct bcm2835_clock_data *data = clock->data;
struct bcm2835_rates *best = NULL;
size_t i;
/* find best matching */
for (i = 0; i < rate_cnt; i++) {
+ /* do not look at anything above the requested rate */
if (rates[i].rate > req->rate)
continue;
+ /* if we have a divider that is not "safe", then ignore */
+ if (divmash_get_divf(rates[i].dmash) &&
+ (rates[i].div < data->min_frac_div))
+ continue;
+ /* if we are the first */
if (!best) {
best = &rates[i];
continue;
@@ -2094,6 +2104,10 @@ static const struct bcm2835_clock_data *bcm2835_register_clock_of(
break;
}
}
+ /* add support for min fractional divider */
+ err = of_property_read_u32(nc, "brcm,min-fract-div", &value);
+ if (!err)
+ data->min_frac_div = value << CM_DIV_FRAC_BITS;
/* and return the result */
return data;
--
1.7.10.4
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