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[PATCH] clk: bcm2835: Correct the prediv logic

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  [PATCH] clk: bcm2835: Correct the prediv logic Eric Anholt <eric@anholt.net> - 2017-05-15 19:40 +0200
    Re: [PATCH] clk: bcm2835: Correct the prediv logic Stefan Wahren <stefan.wahren@i2se.com> - 2017-05-15 19:50 +0200
      Re: [PATCH] clk: bcm2835: Correct the prediv logic Eric Anholt <eric@anholt.net> - 2017-05-15 21:10 +0200

#1641922 — [PATCH] clk: bcm2835: Correct the prediv logic

From: Phil Elwell <phil@raspberrypi.org>

If a clock has the prediv flag set, both the integer and fractional
parts must be scaled when calculating the resulting frequency.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
---

While this is a bugfix, I haven't put a "Fixes:" line in here to get
it automatically backported to stable.  We had trouble with the
out-of-tree DSI panel driver, at least: Our old set_rate() didn't
work, because the new PLL was just barely too fast to get the integer
PLL divider we needed.  We may run into similar troubles
elsewhere. --anholt

 drivers/clk/bcm/clk-bcm2835.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index 025853870619..7a35df6b45bd 100644
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -616,8 +616,10 @@ static unsigned long bcm2835_pll_get_rate(struct clk_hw *hw,
 	using_prediv = cprman_read(cprman, data->ana_reg_base + 4) &
 		data->ana->fb_prediv_mask;
 
-	if (using_prediv)
+	if (using_prediv) {
 		ndiv *= 2;
+		fdiv *= 2;
+	}
 
 	return bcm2835_pll_rate_from_divisors(parent_rate, ndiv, fdiv, pdiv);
 }
-- 
2.11.0

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#1641933

Hi Eric,

> Eric Anholt <eric@anholt.net> hat am 15. Mai 2017 um 19:35 geschrieben:
> 
> 
> From: Phil Elwell <phil@raspberrypi.org>
> 
> If a clock has the prediv flag set, both the integer and fractional
> parts must be scaled when calculating the resulting frequency.
> 
> Signed-off-by: Phil Elwell <phil@raspberrypi.org>
> Signed-off-by: Eric Anholt <eric@anholt.net>
> ---
> 
> While this is a bugfix, I haven't put a "Fixes:" line in here to get
> it automatically backported to stable.  

sorry, i can't follow. How should this happen without "Fixes: "?

> We had trouble with the
> out-of-tree DSI panel driver, at least: Our old set_rate() didn't
> work, because the new PLL was just barely too fast to get the integer
> PLL divider we needed.  We may run into similar troubles
> elsewhere. --anholt
>

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#1641981

[Multipart message — attachments visible in raw view] — view raw

Stefan Wahren <stefan.wahren@i2se.com> writes:

> Hi Eric,
>
>> Eric Anholt <eric@anholt.net> hat am 15. Mai 2017 um 19:35 geschrieben:
>> 
>> 
>> From: Phil Elwell <phil@raspberrypi.org>
>> 
>> If a clock has the prediv flag set, both the integer and fractional
>> parts must be scaled when calculating the resulting frequency.
>> 
>> Signed-off-by: Phil Elwell <phil@raspberrypi.org>
>> Signed-off-by: Eric Anholt <eric@anholt.net>
>> ---
>> 
>> While this is a bugfix, I haven't put a "Fixes:" line in here to get
>> it automatically backported to stable.  
>
> sorry, i can't follow. How should this happen without "Fixes: "?

I didn't want it to be backported to stable, because of the risk.

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