Re: [PATCH RFC]OMAP3:PM:Dynamic Calculation of SDRC stall latency during DVFS

[ambresh <a0393775@ti.com>]

Gurav , Pramod wrote:
> Hi Ambresh,
> 
>>> +	clk_sel_regval = cm_read_mod_reg(PLL_MOD, CM_CLKSEL);
>> *clk already as reference to CM_CLKSEL:
>>
>>   static struct clk dpll3_m2_ck = {
>> [...]
>>          .clksel_reg     = OMAP_CM_REGADDR(PLL_MOD, CM_CLKSEL1),
>>          .clksel_mask    = OMAP3430_CORE_DPLL_CLKOUT_DIV_MASK,
>> [...]
>>
>> so please use .clksel_reg to read the register content.
>>
> 
> This will be done.
> 
>>> +	sys_clk_rate = clk_get_rate(clk_get(NULL, "osc_sys_ck"));
>> Should it be "sys_ck" instead of "osc_sys_ck"?
>>
>> According to my understanding from trm, I guess CLKINP represents DPLL3
>> reference clock (DPLL3_ALWON_FCLK) which is nothing but "sys_ck".
>>
>> Should not make a difference when the sys_clk divisor is 1, but if it is
>> 2, then sys_ck=osc_sys_ck/2.
> 
> 
> Yes, it has to be sys_ck and it will be taken care.
> 
>>> +	/* wait time for L3 clk stabilization = 4*REFCLK + 8*CLKOUTX2 */
>>> +	nr1 = (4 * (core_dpll_div_n + 1) * 2 * core_dpll_clkoutdiv_m2 *
>>> +							 core_dpll_mul_m);
>>> +	nr2 = 8 * (core_dpll_div_n + 1);
>>> +	nr = nr1 + nr2;
>>> +
>>> +	dr = 2 * sys_clk_rate * core_dpll_mul_m * core_dpll_clkoutdiv_m2;
>>> +
>> I am not able to understand the calculations completely for
>> (nr1 + nr2) / dr. and I guess you could simplify the calculation a bit
>> by removing the redundant multiplications and divisions.
>> And also may be you can use m, n & m2 instead of core_dpll_xxx_xx, to
>> make code more readable.
>>

We can get ride of the steps used to calculate CLKOUTX2, by simply 
calling parent's (dpll3_ck) clk->recalc function pointer.

recalc function will return CLKOUT, so CLKOUTX2 = CLKOUT * 2.

pseudo code
------------
struct clk *parent = clk->parent;
clkout = parent->recalc();
clkoutx2 = clkout * 2;

To derive REFCLK. the only unknown parameter will be N, which can be 
read from .clksel_reg.

Why can't we use do_div() api to calculate REFCLK, instead of manual 
calculation?


Regards,
Ambresh




> 
> I am restructuring the formula with appropriate variable names.
> 
> 
> Thank you for your comments.
> 
> Regards,
> Pramod