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[media] smiapp-pll: Add a few comments to PLL calculation

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The PLL calculation heuristics is rather complicated and and is often
difficult to understand to its original author.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Sakari Ailus 2013-08-10 14:49:46 -03:00 committed by Mauro Carvalho Chehab
parent 7be5c28981
commit 367da7a318
1 changed files with 17 additions and 0 deletions
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17
drivers/media/i2c/smiapp-pll.c
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@ -87,6 +87,17 @@ static void print_pll(struct device *dev, struct smiapp_pll *pll)
dev_dbg(dev, "vt_pix_clk_freq_hz \t%d\n", pll->vt_pix_clk_freq_hz);
}
/*
* Heuristically guess the PLL tree for a given common multiplier and
* divisor. Begin with the operational timing and continue to video
* timing once operational timing has been verified.
*
* @mul is the PLL multiplier and @div is the common divisor
* (pre_pll_clk_div and op_sys_clk_div combined). The final PLL
* multiplier will be a multiple of @mul.
*
* @return Zero on success, error code on error.
*/
static int __smiapp_pll_calculate(struct device *dev,
const struct smiapp_pll_limits *limits,
struct smiapp_pll *pll, uint32_t mul,
@ -95,6 +106,12 @@ static int __smiapp_pll_calculate(struct device *dev,
uint32_t sys_div;
uint32_t best_pix_div = INT_MAX >> 1;
uint32_t vt_op_binning_div;
/*
* Higher multipliers (and divisors) are often required than
* necessitated by the external clock and the output clocks.
* There are limits for all values in the clock tree. These
* are the minimum and maximum multiplier for mul.
*/
uint32_t more_mul_min, more_mul_max;
uint32_t more_mul_factor;
uint32_t min_vt_div, max_vt_div, vt_div;