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SubjectRe: [PATCH v4 2/3] PM / devfreq: tegra: add devfreq driver for Tegra Activity Monitor
Hi

I have not reviewed this code closely, but a few items just caught my eye
at a brief glance.

On Tue, 9 Dec 2014, Tomeu Vizoso wrote:

> The ACTMON block can monitor several counters, providing averaging and firing
> interrupts based on watermarking configuration. This implementation monitors
> the MCALL and MCCPU counters to choose an appropriate frequency for the
> external memory clock.
>
> This patch is based on work by Alex Frid <afrid@nvidia.com> and Mikko
> Perttunen <mikko.perttunen@kapsi.fi>.

It's important to put people in the Cc: section, either when you're basing
your code off of their work, or when you mention them in the patch
description. This means including specific Cc: lines in the
Signed-off-by: section at the bottom of the patch -- not just mentioning
them in the patch description. That way, any further followup from others
after the patch is committed is more likely to be appropriately copied to
those people.

For some reason this doesn't happen with many Tegra upstream-bound patches
-- from a variety of submitters, including NVIDIA submitters! -- but it
needs to start happening.

Also I see that Aleks Frid wasn't cc'ed at all in the E-mail headers;
fixing at least that point.

> +static struct tegra_devfreq_device_config actmon_device_configs[] = {
> + {
> + /* MCALL: All memory accesses (including from the CPUs) */
> + .offset = 0x1c0,
> + .irq_mask = 1 << 26,
> + .boost_up_coeff = 200,
> + .boost_down_coeff = 50,
> + .boost_up_threshold = 60,
> + .boost_down_threshold = 40,
> + },
> + {
> + /* MCCPU: memory accesses from the CPUs */
> + .offset = 0x200,
> + .irq_mask = 1 << 25,
> + .boost_up_coeff = 800,
> + .boost_down_coeff = 90,
> + .boost_up_threshold = 27,
> + .boost_down_threshold = 10,
> + .avg_dependency_threshold = 50000,
> + },
> +};

This data represents PM policy. In other words, it is use-case sensitive.
Different users may wish to change these values depending on their
application characteristics -- and it does not represent unchangeable
hardware fact.

On the other hand...

> +static u32 actmon_readl(struct tegra_devfreq *tegra, u32 offset)
> +{
> + return readl(tegra->regs + offset);
> +}
> +
> +static void actmon_writel(struct tegra_devfreq *tegra, u32 val, u32 offset)
> +{
> + writel(val, tegra->regs + offset);
> +}
> +
> +static u32 device_readl(struct tegra_devfreq_device *dev, u32 offset)
> +{
> + return readl(dev->regs + offset);
> +}
> +
> +static void device_writel(struct tegra_devfreq_device *dev, u32 val,
> + u32 offset)
> +{
> + writel(val, dev->regs + offset);
> +}
> +
> +static unsigned long do_percent(unsigned long val, unsigned int pct)
> +{
> + return val * pct / 100;
> +}
> +
> +static void tegra_devfreq_update_avg_wmark(struct tegra_devfreq *tegra,
> + struct tegra_devfreq_device *dev)
> +{
> + u32 avg = dev->avg_count;
> + u32 avg_band_freq = tegra->max_freq * ACTMON_DEFAULT_AVG_BAND / KHZ;
> + u32 band = avg_band_freq * ACTMON_SAMPLING_PERIOD;
> +
> + device_writel(dev, avg + band, ACTMON_DEV_AVG_UPPER_WMARK);
> +
> + avg = max(dev->avg_count, band);
> + device_writel(dev, avg - band, ACTMON_DEV_AVG_LOWER_WMARK);
> +}
> +
> +static void tegra_devfreq_update_wmark(struct tegra_devfreq *tegra,
> + struct tegra_devfreq_device *dev)
> +{
> + u32 val = tegra->cur_freq * ACTMON_SAMPLING_PERIOD;
> +
> + device_writel(dev, do_percent(val, dev->config->boost_up_threshold),
> + ACTMON_DEV_UPPER_WMARK);
> +
> + device_writel(dev, do_percent(val, dev->config->boost_down_threshold),
> + ACTMON_DEV_LOWER_WMARK);
> +}
> +
> +static void actmon_write_barrier(struct tegra_devfreq *tegra)
> +{
> + /* ensure the update has reached the ACTMON */
> + wmb();
> + actmon_readl(tegra, ACTMON_GLB_STATUS);
> +}
> +
> +static irqreturn_t actmon_isr(int irq, void *data)
> +{
> + struct tegra_devfreq *tegra = data;
> + struct tegra_devfreq_device *dev = NULL;
> + unsigned long flags;
> + u32 val, intr_status, dev_ctrl;
> + unsigned int i;
> +
> + val = actmon_readl(tegra, ACTMON_GLB_STATUS);
> +
> + for (i = 0; i < ARRAY_SIZE(tegra->devices); i++) {
> + if (val & tegra->devices[i].config->irq_mask) {
> + dev = tegra->devices + i;
> + break;
> + }
> + }
> +
> + if (!dev)
> + return IRQ_NONE;
> +
> + spin_lock_irqsave(&tegra->lock, flags);
> +
> + dev->avg_count = device_readl(dev, ACTMON_DEV_AVG_COUNT);
> + tegra_devfreq_update_avg_wmark(tegra, dev);
> +
> + intr_status = device_readl(dev, ACTMON_DEV_INTR_STATUS);
> + dev_ctrl = device_readl(dev, ACTMON_DEV_CTRL);
> +
> + if (intr_status & ACTMON_DEV_INTR_CONSECUTIVE_UPPER) {
> + /*
> + * new_boost = min(old_boost * up_coef + step, max_freq)
> + */
> + dev->boost_freq = do_percent(dev->boost_freq,
> + dev->config->boost_up_coeff);
> + dev->boost_freq += ACTMON_BOOST_FREQ_STEP;
> +
> + dev_ctrl |= ACTMON_DEV_CTRL_CONSECUTIVE_BELOW_WMARK_EN;
> +
> + if (dev->boost_freq >= tegra->max_freq)
> + dev->boost_freq = tegra->max_freq;
> + else
> + dev_ctrl |= ACTMON_DEV_CTRL_CONSECUTIVE_ABOVE_WMARK_EN;
> + } else if (intr_status & ACTMON_DEV_INTR_CONSECUTIVE_LOWER) {
> + /*
> + * new_boost = old_boost * down_coef
> + * or 0 if (old_boost * down_coef < step / 2)
> + */
> + dev->boost_freq = do_percent(dev->boost_freq,
> + dev->config->boost_down_coeff);
> +
> + dev_ctrl |= ACTMON_DEV_CTRL_CONSECUTIVE_ABOVE_WMARK_EN;
> +
> + if (dev->boost_freq < (ACTMON_BOOST_FREQ_STEP >> 1))
> + dev->boost_freq = 0;
> + else
> + dev_ctrl |= ACTMON_DEV_CTRL_CONSECUTIVE_BELOW_WMARK_EN;
> + }
> +
> + if (dev->config->avg_dependency_threshold) {
> + if (dev->avg_count >= dev->config->avg_dependency_threshold)
> + dev_ctrl |= ACTMON_DEV_CTRL_CONSECUTIVE_BELOW_WMARK_EN;
> + else if (dev->boost_freq == 0)
> + dev_ctrl &= ~ACTMON_DEV_CTRL_CONSECUTIVE_BELOW_WMARK_EN;
> + }
> +
> + device_writel(dev, dev_ctrl, ACTMON_DEV_CTRL);
> +
> + device_writel(dev, ACTMON_INTR_STATUS_CLEAR, ACTMON_DEV_INTR_STATUS);
> +
> + actmon_write_barrier(tegra);
> +
> + spin_unlock_irqrestore(&tegra->lock, flags);
> +
> + return IRQ_WAKE_THREAD;
> +}

... all this code is clearly low level device driver code and is intended
to represent immutable hardware fact. It is use-case independent, PM
policy-invariant, and in theory should be verifiable against the Tegra TRM
(or whatever).

The policy code and data should be separated into a separate file and/or
subsystem from the low-level ACTMON device driver. The policy code should
be easily swappable or tunable by end-users without touching the
underlying device driver.

So these entities should use some kind of Linux generic subsystem/function
call interface to loosely couple the policy with the low-level device
driver. I have not combed the tree to see what makes the most sense. But
the perf subsystem comes to mind as one strong candidate.


- Paul


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