Re: [PATCH v2 2/4] PM / OPP: Initialize OPP table from device tree

[Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 08/05/2012 10:05 AM, Shawn Guo wrote:
> With a lot of devices booting from device tree nowadays, it requires
> that OPP table can be initialized from device tree.  The patch adds
> a helper function of_init_opp_table together with a binding doc for
> that purpose.
> 
> Signed-off-by: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/power/opp.txt |   25 +++++++++
>  drivers/base/power/opp.c                        |   65 +++++++++++++++++++++++
>  include/linux/opp.h                             |    8 +++
>  3 files changed, 98 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/power/opp.txt
> 
> diff --git a/Documentation/devicetree/bindings/power/opp.txt b/Documentation/devicetree/bindings/power/opp.txt
> new file mode 100644
> index 0000000..2238520
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/opp.txt
> @@ -0,0 +1,25 @@
> +* Generic OPP Interface
> +
> +SoCs have a standard set of tuples consisting of frequency and
> +voltage pairs that the device will support per voltage domain. These
> +are called Operating Performance Points or OPPs.
> +
> +Properties:
> +- operating-points: An array of 3-tuples items, and each item consists

3 tuples?

> +  of frequency and voltage like <freq-kHz vol-uV>.
> +	freq: clock frequency in kHz
> +	vol: voltage in microvolt

Although maybe 3 fields would be good for a flags field? I'm concerned
it's a pretty generic name and not very future proof. What about
transition times? Not sure how you would represent that as it probably
depends on which points you are changing between rather than a property
of the opp.

I'm not saying we have to address that now, but just have some path in
the future.

> +
> +Examples:
> +
> +cpu@0 {
> +	compatible = "arm,cortex-a9";
> +	reg = <0>;
> +	next-level-cache = <&L2>;
> +	operating-points = <
> +		/* kHz    uV */
> +		792000  1100000
> +		396000  950000
> +		198000  850000
> +	>;
> +};
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index ac993ea..1bf1be8 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -22,6 +22,7 @@
>  #include <linux/rculist.h>
>  #include <linux/rcupdate.h>
>  #include <linux/opp.h>
> +#include <linux/of.h>
>  
>  /*
>   * Internal data structure organization with the OPP layer library is as
> @@ -674,3 +675,67 @@ struct srcu_notifier_head *opp_get_notifier(struct device *dev)
>  
>  	return &dev_opp->head;
>  }
> +
> +#ifdef CONFIG_OF
> +/**
> + * of_init_opp_table() - Initialize opp table from device tree
> + * @dev:	device pointer used to lookup device OPPs.
> + *
> + * Register the initial OPP table with the OPP library for given device.
> + */
> +int of_init_opp_table(struct device *dev)
> +{
> +	struct device_node *np = dev->of_node;
> +	const char *propname = "operating-points";
> +	const struct property *pp;
> +	u32 *opp;
> +	int ret, i, nr;
> +
> +	pp = of_find_property(np, propname, NULL);
> +	if (!pp) {
> +		dev_err(dev, "%s: Unable to find property", __func__);
> +		return -ENODEV;
> +	}
> +
> +	opp = kzalloc(pp->length, GFP_KERNEL);
> +	if (!opp) {
> +		dev_err(dev, "%s: Unable to allocate array\n", __func__);
> +		return -ENOMEM;
> +	}
> +
> +	nr = pp->length / sizeof(u32);
> +	ret = of_property_read_u32_array(np, propname, opp, nr);
> +	if (ret) {
> +		dev_err(dev, "%s: Unable to read OPPs\n", __func__);
> +		goto out;
> +	}
> +
> +	if (nr % 2) {
> +		dev_err(dev, "%s: Invalid OPP list\n", __func__);
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	nr /= 2;
> +	for (i = 0; i < nr; i++) {
> +		/*
> +		 * Each OPP is a set of tuples consisting of frequency and
> +		 * voltage like <freq-kHz vol-uV>.
> +		 */
> +		u32 *val = opp + i * 2;
> +
> +		val[0] *= 1000;
> +		ret = opp_add(dev, val[0], val[1]);
> +		if (ret) {
> +			dev_warn(dev, "%s: Failed to add OPP %d: %d\n",
> +				 __func__, val[0], ret);
> +			continue;
> +		}
> +	}

I think this whole function can be written more concisely. Just iterate
over the property and avoid the intermediate array allocation.

Rob