linux-kernel - Re: [PATCH] clk: si5351: Add setup steps

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Date:	Fri, 20 Nov 2015 09:18:57 +0100
From:	Jacob Siverskog <jacob@...nage.engineering>
To:	Belisko Marek <marek.belisko@...il.com>
Cc:	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-clk@...r.kernel.org,
	Jens Rudberg <jens@...nage.engineering>
Subject: Re: [PATCH] clk: si5351: Add setup steps

Hi Marek!
Thanks for your feedback.

On Thu, Nov 19, 2015 at 3:18 PM, Belisko Marek <marek.belisko@...il.com> wrote:
> Hi Jacob,
>
> On Thu, Nov 19, 2015 at 2:40 PM, Jacob Siverskog
> <jacob@...nage.engineering> wrote:
>> This is according to figure 12 ("I2C Programming Procedure") in
>> "Si5351A/B/C Data Sheet"
>> (https://www.silabs.com/Support%20Documents/TechnicalDocs/Si5351-B.pdf).
>>
>> Without the PLL soft reset, we were unable to get three outputs
>> working at the same time.
>>
>> According to Silicon Labs support, performing PLL soft reset will only
>> be noticable if the PLL parameters have been changed.
>>
>> Signed-off-by: Jacob Siverskog <jacob@...nage.engineering>
>> Signed-off-by: Jens Rudberg <jens@...nage.engineering>
>> ---
>>  drivers/clk/clk-si5351.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/drivers/clk/clk-si5351.c b/drivers/clk/clk-si5351.c
>> index e346b22..110de35 100644
>> --- a/drivers/clk/clk-si5351.c
>> +++ b/drivers/clk/clk-si5351.c
>> @@ -1091,6 +1091,11 @@ static int si5351_clkout_set_rate(struct clk_hw *hw, unsigned long rate,
>>         si5351_set_bits(hwdata->drvdata, SI5351_CLK0_CTRL + hwdata->num,
>>                         SI5351_CLK_POWERDOWN, 0);
>>
>> +       /* do a pll soft reset on both plls, needed in some cases to get all
>> +        * outputs running */
>           ^^^^ wrong format of multi line comment, please look at
> Documentation/CodingStyle
>> +       si5351_reg_write(hwdata->drvdata, SI5351_PLL_RESET,
>> +                        SI5351_PLL_RESET_A | SI5351_PLL_RESET_B);
>          ^^^^ according datasheet PLL_RESET_A/B are self clearing bits
> valid for Si5351A/C only
>          so probably we need to add some code for B model

Well, this is interesting. In the latest data sheet (that I've
been reading,
https://www.silabs.com/Support%20Documents/TechnicalDocs/Si5351-B.pdf),
this is not mentioned at all. For the register descriptions, it
only refers to "AN619 Generating a register
map" (http://www.silabs.com/Support%20Documents/TechnicalDocs/AN619.pdf),
where no such caveat exists. I found an old datasheet on my
computer that has the same phrasing as yours.

I have sent an e-mail to our SiLabs representative regarding this
matter.

>> +
>>         dev_dbg(&hwdata->drvdata->client->dev,
>>                 "%s - %s: rdiv = %u, parent_rate = %lu, rate = %lu\n",
>>                 __func__, clk_hw_get_name(hw), (1 << rdiv),
>> @@ -1359,6 +1364,14 @@ static int si5351_i2c_probe(struct i2c_client *client,
>>                 return PTR_ERR(drvdata->regmap);
>>         }
>>
>> +       /* Disable outputs */
>> +       si5351_reg_write(drvdata, SI5351_OUTPUT_ENABLE_CTRL, 0xff);
>> +
>> +       /* Power down all output drivers */
>> +       for (n = 0; n < 8; n++) {
>> +               si5351_reg_write(drvdata, SI5351_CLK0_CTRL + n, 0x80);
>> +       }
>             ^^^ single line after for statement doesn't need curly
> braces (if you run ./scripts/check_patch it will complain)

I will fix all embarrassing cosmetic issues for the next version of the patch.

>> +
>>         /* Disable interrupts */
>>         si5351_reg_write(drvdata, SI5351_INTERRUPT_MASK, 0xf0);
>>         /* Ensure pll select is on XTAL for Si5351A/B */
>> --
>> 2.6.3
>>
>> --
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>
> BR,
>
> marek
>
> --
> as simple and primitive as possible
> -------------------------------------------------
> Marek Belisko - OPEN-NANDRA
> Freelance Developer
>
> Ruska Nova Ves 219 | Presov, 08005 Slovak Republic
> Tel: +421 915 052 184
> skype: marekwhite
> twitter: #opennandra
> web: http://open-nandra.com

Thanks, Jacob
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