[PATCH] ARM: S3C24XX: Add .get_rate callback for "camif-upll" clock

On 08/28/2012 12:58 AM, Kukjin Kim wrote:

On 08/27/12 13:12, Sylwester Nawrocki wrote:

quoted

Add missing get_rate callback for the "camif-upll" clock, so frequency
of this clock is properly reported with clk_get_rate().

Signed-off-by: Sylwester Nawrocki<sylvester.nawrocki@gmail.com>
---
arch/arm/mach-s3c24xx/clock-s3c2440.c | 14 ++++++++++++++
1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mach-s3c24xx/clock-s3c2440.c 

b/arch/arm/mach-s3c24xx/clock-s3c2440.c
index cb2883d..749220f 100644

--- a/arch/arm/mach-s3c24xx/clock-s3c2440.c
+++ b/arch/arm/mach-s3c24xx/clock-s3c2440.c

@@ -87,6 +87,19 @@ static int s3c2440_camif_upll_setrate(struct clk 

*clk, unsigned long rate)
return 0;
}

+static unsigned long s3c2440_camif_upll_getrate(struct clk *clk)
+{
+ unsigned long parent_rate = clk_get_rate(clk->parent);
+ unsigned long camdivn = __raw_readl(S3C2440_CAMDIVN);
+
+ if (!(camdivn& S3C2440_CAMDIVN_CAMCLK_SEL))
+ return parent_rate;
+
+ camdivn&= S3C2440_CAMDIVN_CAMCLK_MASK;
+
+ return parent_rate / (camdivn + 1) / 2;

Well, why do we need '/ 2' here?

I simply followed documentation of the camera clock divider register
(CAMDIVN). This is how CAMCLK_SEL and CAMCLK_DIV bit fields are described
there:

CAMDIVN      |  Bit  |       Description
--------------------------------------------------------------------------
CAMCLK_SEL   | [4]   | 0 : Use CAMCLK with UPLL output(CAMCLK=UPLL output)
             |       | 1 : CAMCLK is divided by CAMCLK_DIV value
-------------+-------+----------------------------------------------------
CAMCLK_DIV   | [3:0] | CAMCLK divide factor setting register(0 ? 15).
             |       | Camera clock = UPLL / [(CAMCLK_DIV +1)x2].
             |       | This bit is valid when CAMCLK_SEL=1.

So, camera clock frequency = parent_rate / ((camdivn + 1) * 2).
This is exactly same as 'parent_rate / ( camdivn + 1) / 2'.

To be 1000% sure I compared frequency values reported from clk_get_rate()
in the driver with values measured with an oscilloscope at the CAMCLKOUT
pin. Everything was as expected (UPLL - 48 MHz, CAMCLKOUT - 12 MHz).

Also, it's easy to confirm correctness of this code by inversing equations
found in function s3c2440_camif_upll_setrate(), i.e.

 camdivn &= ~(S3C2440_CAMDIVN_CAMCLK_SEL | S3C2440_CAMDIVN_CAMCLK_MASK);
 if (rate != parent_rate) {
 	camdivn |= S3C2440_CAMDIVN_CAMCLK_SEL;
 	camdivn |= (((parent_rate / rate) / 2) - 1);
 }

 __raw_writel(camdivn, S3C2440_CAMDIVN);

--
Regards,
Sylwester