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clk: si5351: Apply PLL soft reset before enabling the outputs

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The "Si5351A/B/C Data Sheet" states to apply a PLL soft reset before
enabling the output clocks [1]. This is required to get a deterministic
phase relationship between the output clocks.

Without resetting the PLL, the phase relationship between the clocks is
unpredictable. Fix this by resetting the PLL in si5351_clkout_prepare().

References:
[1] https://www.silabs.com/Support%20Documents/TechnicalDocs/Si5351-B.pdf
    Figure 12 ("I2C Programming Procedure")

Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Rabeeh Khoury <rabeeh@solid-run.com>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Sergej Sawazki <sergej@taudac.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
This commit is contained in:
Sergej Sawazki 2017-09-16 13:44:42 +02:00 committed by Stephen Boyd
parent 51279ef9f6
commit b26ff127c5
1 changed files with 29 additions and 0 deletions
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29
drivers/clk/clk-si5351.c
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@ -903,13 +903,42 @@ static int _si5351_clkout_set_disable_state(
return 0;
}
void _si5351_clkout_reset_pll(struct si5351_driver_data *drvdata, int num)
{
u8 val = si5351_reg_read(drvdata, SI5351_CLK0_CTRL + num);
switch (val & SI5351_CLK_INPUT_MASK) {
case SI5351_CLK_INPUT_XTAL:
case SI5351_CLK_INPUT_CLKIN:
return; /* pll not used, no need to reset */
}
si5351_reg_write(drvdata, SI5351_PLL_RESET,
val & SI5351_CLK_PLL_SELECT ? SI5351_PLL_RESET_B :
SI5351_PLL_RESET_A);
dev_dbg(&drvdata->client->dev, "%s - %s: pll = %d\n",
__func__, clk_hw_get_name(&drvdata->clkout[num].hw),
(val & SI5351_CLK_PLL_SELECT) ? 1 : 0);
}
static int si5351_clkout_prepare(struct clk_hw *hw)
{
struct si5351_hw_data *hwdata =
container_of(hw, struct si5351_hw_data, hw);
struct si5351_platform_data *pdata =
hwdata->drvdata->client->dev.platform_data;
si5351_set_bits(hwdata->drvdata, SI5351_CLK0_CTRL + hwdata->num,
SI5351_CLK_POWERDOWN, 0);
/*
* Do a pll soft reset on the parent pll -- needed to get a
* deterministic phase relationship between the output clocks.
*/
if (pdata->clkout[hwdata->num].pll_reset)
_si5351_clkout_reset_pll(hwdata->drvdata, hwdata->num);
si5351_set_bits(hwdata->drvdata, SI5351_OUTPUT_ENABLE_CTRL,
(1 << hwdata->num), 0);
return 0;