Re: [PATCH v6 09/14] memory: tegra: Add EMC scaling support code for Tegra210

[Dmitry Osipenko <digetx@gmail.com>]

09.04.2020 20:52, Thierry Reding пишет:
...
> +static int tegra210_emc_set_rate(struct device *dev,
> +				 const struct tegra210_clk_emc_config *config)
> +{
> +	struct tegra210_emc *emc = dev_get_drvdata(dev);
> +	struct tegra210_emc_timing *timing = NULL;
> +	unsigned long rate = config->rate;
> +	s64 last_change_delay;
> +	unsigned long flags;
> +	unsigned int i;
> +
> +	if (rate == emc->last->rate * 1000UL)
> +		return 0;

Couldn't all the rates be expressed in Hz? Then you won't need all these
multiplications by 1000.

> +	for (i = 0; i < emc->num_timings; i++) {
> +		if (emc->timings[i].rate * 1000UL == rate) {
> +			timing = &emc->timings[i];
> +			break;
> +		}
> +	}
> +
> +	if (!timing)
> +		return -EINVAL;
> +
> +	if (rate > 204000000 && !timing->trained)
> +		return -EINVAL;
> +
> +	emc->next = timing;
> +	last_change_delay = ktime_us_delta(ktime_get(), emc->clkchange_time);
> +
> +	/* XXX use non-busy-looping sleep? */
> +	if ((last_change_delay >= 0) &&
> +	    (last_change_delay < emc->clkchange_delay))
> +		udelay(emc->clkchange_delay - (int)last_change_delay);
> +
> +	spin_lock_irqsave(&emc->lock, flags);
> +	tegra210_emc_set_clock(emc, config->value);
> +	emc->clkchange_time = ktime_get();
> +	emc->last = timing;
> +	spin_unlock_irqrestore(&emc->lock, flags);
> +
> +	return 0;
> +}

I'd suggest to check how much time invocation of ktime_get() takes, at
least it came to a surprise to me in a case of the tegra-cpuidle driver.

It may be well over the emc->clkchange_delay.

...
> +static int tegra210_emc_probe(struct platform_device *pdev)
> +{
...
> +	emc->clkchange_delay = 100;
> +	emc->training_interval = 100;

Not sure why these aren't a constant with the code.. ?