Re: [PATCH v2 06/14] ARM: sun8i: clk: Add clk-factor rate application method

["Ondřej Jirman" <megous@megous.com>]

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On 30.6.2016 22:40, Maxime Ripard wrote:
> Hi,
> 
> On Sat, Jun 25, 2016 at 05:45:03AM +0200, megous@megous.com wrote:
>> From: Ondrej Jirman <megous@megous.com>
>>
>> PLL1 on H3 requires special factors application algorithm,
>> when the rate is changed. This algorithm was extracted
>> from the arisc code that handles frequency scaling
>> in the BSP kernel.
>>
>> This commit adds optional apply function to
>> struct factors_data, that can implement non-trivial
>> factors application method, when necessary.
>>
>> Also struct clk_factors_config is extended with position
>> of the PLL lock flag.
> 
> Have you tested the current implementation, and found that it was not
> working, or did you duplicate the arisc code directly?

Also of note is that similar code probably doesn't crash in u-boot,
because there, before changing the PLL1 clock, the cpu is switched to
24MHz osc, so it is not overclocked, even if factors align in such a way
that you'd get the behavior I described in the other email.

>>  /**
>> + * sun8i_h3_apply_pll1_factors() - applies n, k, m, p factors to the
>> + * register using an algorithm that tries to reserve the PLL lock
>> + */
>> +
>> +static void sun8i_h3_apply_pll1_factors(struct clk_factors *factors, struct factors_request *req)
>> +{
>> +	const struct clk_factors_config *config = factors->config;
>> +	u32 reg;
>> +
>> +	/* Fetch the register value */
>> +	reg = readl(factors->reg);
>> +
>> +	if (FACTOR_GET(config->pshift, config->pwidth, reg) < req->p) {
>> +		reg = FACTOR_SET(config->pshift, config->pwidth, reg, req->p);
>> +
>> +		writel(reg, factors->reg);
>> +		__delay(2000);
>> +	}
> 
> So there was some doubts about the fact that P was being used, or at
> least that it was useful.
> 
>> +	if (FACTOR_GET(config->mshift, config->mwidth, reg) < req->m) {
>> +		reg = FACTOR_SET(config->mshift, config->mwidth, reg, req->m);
>> +
>> +		writel(reg, factors->reg);
>> +		__delay(2000);
>> +	}
>> +
>> +	reg = FACTOR_SET(config->nshift, config->nwidth, reg, req->n);
>> +	reg = FACTOR_SET(config->kshift, config->kwidth, reg, req->k);
>> +
>> +	writel(reg, factors->reg);
>> +	__delay(20);
>> +
>> +	while (!(readl(factors->reg) & (1 << config->lock)));
> 
> So, they are applying the dividers first, and then applying the
> multipliers, and then wait for the PLL to stabilize.
> 
>> +
>> +	if (FACTOR_GET(config->mshift, config->mwidth, reg) > req->m) {
>> +		reg = FACTOR_SET(config->mshift, config->mwidth, reg, req->m);
>> +
>> +		writel(reg, factors->reg);
>> +		__delay(2000);
>> +	}
>> +
>> +	if (FACTOR_GET(config->pshift, config->pwidth, reg) > req->p) {
>> +		reg = FACTOR_SET(config->pshift, config->pwidth, reg, req->p);
>> +
>> +		writel(reg, factors->reg);
>> +		__delay(2000);
>> +	}
> 
> However, this is kind of weird, why would you need to re-apply the
> dividers? Nothing really changes. Have you tried without that part?
> 
> Since this is really specific, I guess you could simply make the
> clk_ops for the nkmp clocks public, and just re-implement set_rate
> using that logic.
> 
> You might also need to set an upper limit on P, since the last value
> (4) is not a valid one.
> 
> I guess you could do that by adding a max field in the __ccu_div
> structure.
> 
> Maxime
> 


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