Re: [RFC PATCH v3 5/7] devfreq: exynos-bus: Add interconnect functionality to exynos-bus

[Chanwoo Choi]

On Sun, Dec 22, 2019 at 4:53 AM Chanwoo Choi <chanwoo@xxxxxxxxxx> wrote:
>
> Hi,
>
> On Fri, Dec 20, 2019 at 9:02 PM Artur ÅwigoÅ <a.swigon@xxxxxxxxxxx> wrote:
> >
> > This patch adds interconnect functionality to the exynos-bus devfreq
> > driver.
> >
> > The SoC topology is a graph (or, more specifically, a tree) and its
> > edges are specified using the 'exynos,interconnect-parent-node' in the
> > DT. Due to unspecified relative probing order, -EPROBE_DEFER may be
> > propagated to ensure that the parent is probed before its children.
> >
> > Each bus is now an interconnect provider and an interconnect node as well
> > (cf. Documentation/interconnect/interconnect.rst), i.e. every bus registers
> > itself as a node. Node IDs are not hardcoded but rather assigned at
> > runtime, in probing order (subject to the above-mentioned exception
> > regarding relative order). This approach allows for using this driver with
> > various Exynos SoCs.
> >
> > Frequencies requested via the interconnect API for a given node are
> > propagated to devfreq using dev_pm_qos_update_request(). Please note that
> > it is not an error when CONFIG_INTERCONNECT is 'n', in which case all
> > interconnect API functions are no-op.
> >
> > Signed-off-by: Artur ÅwigoÅ <a.swigon@xxxxxxxxxxx>
> > ---
> >  drivers/devfreq/exynos-bus.c | 144 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 144 insertions(+)
> >
> > diff --git a/drivers/devfreq/exynos-bus.c b/drivers/devfreq/exynos-bus.c
> > index 9fdb188915e8..694a9581dcdb 100644
> > --- a/drivers/devfreq/exynos-bus.c
> > +++ b/drivers/devfreq/exynos-bus.c
> > @@ -14,14 +14,19 @@
> >  #include <linux/devfreq-event.h>
> >  #include <linux/device.h>
> >  #include <linux/export.h>
> > +#include <linux/idr.h>
> > +#include <linux/interconnect-provider.h>
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/pm_opp.h>
> > +#include <linux/pm_qos.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/regulator/consumer.h>
> >
> >  #define DEFAULT_SATURATION_RATIO       40
> >
> > +#define kbps_to_khz(x) ((x) / 8)
> > +
> >  struct exynos_bus {
> >         struct device *dev;
> >
> > @@ -35,6 +40,12 @@ struct exynos_bus {
> >         struct opp_table *opp_table;
> >         struct clk *clk;
> >         unsigned int ratio;
> > +
> > +       /* One provider per bus, one node per provider */
> > +       struct icc_provider provider;
> > +       struct icc_node *node;
> > +
> > +       struct dev_pm_qos_request qos_req;
> >  };
> >
> >  /*
> > @@ -205,6 +216,39 @@ static void exynos_bus_passive_exit(struct device *dev)
> >         clk_disable_unprepare(bus->clk);
> >  }
> >
> > +static int exynos_bus_icc_set(struct icc_node *src, struct icc_node *dst)
> > +{
> > +       struct exynos_bus *src_bus = src->data, *dst_bus = dst->data;
> > +       s32 src_freq = kbps_to_khz(src->avg_bw);
> > +       s32 dst_freq = kbps_to_khz(dst->avg_bw);
> > +       int ret;
> > +
> > +       ret = dev_pm_qos_update_request(&src_bus->qos_req, src_freq);
> > +       if (ret < 0) {
> > +               dev_err(src_bus->dev, "failed to update PM QoS request");
>
> To catch the correct error point, better to add 'src node' to error message
> as following:
>
> dev_err(src_bus->dev, "failed to update PM QoS of %s\n",
>                                                dev_name(src_bus->dev.parent))
>
> > +               return ret;
> > +       }
> > +
> > +       ret = dev_pm_qos_update_request(&dst_bus->qos_req, dst_freq);
> > +       if (ret < 0) {
> > +               dev_err(dst_bus->dev, "failed to update PM QoS request");
>
> ditto.
>
> dev_err(src_bus->dev, "failed to update PM QoS of %s\n",
>                                                dev_name(dst_bus->dev.parent))
>
>
> > +               return ret;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static struct icc_node *exynos_bus_icc_xlate(struct of_phandle_args *spec,
> > +                                            void *data)
> > +{
> > +       struct exynos_bus *bus = data;
> > +
> > +       if (spec->np != bus->dev->of_node)
> > +               return ERR_PTR(-EINVAL);
> > +
> > +       return bus->node;
> > +}
> > +
> >  static int exynos_bus_parent_parse_of(struct device_node *np,
> >                                         struct exynos_bus *bus)
> >  {
> > @@ -419,6 +463,96 @@ static int exynos_bus_profile_init_passive(struct exynos_bus *bus,
> >         return 0;
> >  }
> >
> > +static struct icc_node *exynos_bus_icc_get_parent(struct exynos_bus *bus)
> > +{
> > +       struct device_node *np = bus->dev->of_node;
> > +       struct of_phandle_args args;
> > +       int num, ret;
> > +
> > +       num = of_count_phandle_with_args(np, "exynos,interconnect-parent-node",
> > +                                       "#interconnect-cells");
> > +       if (num != 1)
> > +               return NULL; /* parent nodes are optional */
>
> You better to add the comment before calling exynos_bus_icc_get_parent
> and remove '/* parent nodes are optional */'. Actually, it is not enough
> to understand the role of 'interconnect-parent-node' with '/* parent
> nodes are optional */'.
> And I add my opinion about this comment below.
>
> And I expect that you will add the description and example for
> 'exynos,interconnect-parent-node' on exynos-bus dt-binding document.
>
> > +
> > +       ret = of_parse_phandle_with_args(np, "exynos,interconnect-parent-node",
> > +                                       "#interconnect-cells", 0, &args);
> > +       if (ret < 0)
> > +               return ERR_PTR(ret);
> > +
> > +       of_node_put(args.np);
> > +
> > +       return of_icc_get_from_provider(&args);
> > +}
> > +
> > +static int exynos_bus_icc_init(struct exynos_bus *bus)
> > +{
> > +       static DEFINE_IDA(ida);
> > +
> > +       struct device *dev = bus->dev;
> > +       struct icc_provider *provider = &bus->provider;
> > +       struct icc_node *node, *parent_node;
> > +       int id, ret;
> > +
> > +       /* Initialize the interconnect provider */
> > +       provider->set = exynos_bus_icc_set;
> > +       provider->aggregate = icc_std_aggregate;
> > +       provider->xlate = exynos_bus_icc_xlate;
> > +       provider->dev = dev;
> > +       provider->inter_set = true;
> > +       provider->data = bus;
> > +
> > +       ret = icc_provider_add(provider);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       ret = id = ida_alloc(&ida, GFP_KERNEL);
> > +       if (ret < 0)
> > +               goto err_id;
> > +
> > +       node = icc_node_create(id);
> > +       if (IS_ERR(node)) {
> > +               ret = PTR_ERR(node);
> > +               goto err_node;
> > +       }
> > +
> > +       bus->node = node;
> > +       node->name = dev->of_node->name;
> > +       node->data = bus;
> > +       icc_node_add(node, provider);
> > +
>
> Better to add the following comment. If you add following comment
> before calling exynos_bus_icc_get_parent, don't need to add the
> same comment into exynos_bus_icc.
>     /* If interconnect parent node is not existing, don't use
> interconnect feature */
>
> > +       parent_node = exynos_bus_icc_get_parent(bus);
> > +       if (IS_ERR(parent_node)) {
> > +               ret = PTR_ERR(parent_node);
> > +               goto err_parent;
> > +       }
> > +
> > +       if (parent_node) {
>
> Better to change this if statement as following:
> else if (parent_node)
>
>
> > +               ret = icc_link_create(node, parent_node->id);
> > +               if (ret < 0)
> > +                       goto err_parent;
> > +       }
> > +
> > +       ret = dev_pm_qos_add_request(bus->devfreq->dev.parent, &bus->qos_req,
> > +                                       DEV_PM_QOS_MIN_FREQUENCY, 0);
>
> Is it necessary if interconnect-parent-node is not existing?

I realized it is necessary for final destination node.

>
>
> > +       if (ret < 0)
> > +               goto err_request;
> > +
> > +       return 0;
> > +
> > +err_request:
> > +       if (parent_node)
> > +               icc_link_destroy(node, parent_node);
> > +err_parent:
> > +       icc_node_del(node);
> > +       icc_node_destroy(id);
> > +err_node:
> > +       ida_free(&ida, id);
> > +err_id:
> > +       icc_provider_del(provider);
> > +
> > +       return ret;
> > +}
> > +
> >  static int exynos_bus_probe(struct platform_device *pdev)
> >  {
> >         struct device *dev = &pdev->dev;
> > @@ -468,6 +602,16 @@ static int exynos_bus_probe(struct platform_device *pdev)
> >         if (ret < 0)
> >                 goto err;
> >
> > +       /*
> > +        * Initialize interconnect provider. A return value of -ENOTSUPP means
> > +        * that CONFIG_INTERCONNECT is disabled.
> > +        */
> > +       ret = exynos_bus_icc_init(bus);
> > +       if (ret < 0 && ret != -ENOTSUPP) {
> > +               dev_err(dev, "failed to initialize the interconnect provider");
> > +               goto err;
> > +       }
> > +
> >         max_state = bus->devfreq->profile->max_state;
> >         min_freq = (bus->devfreq->profile->freq_table[0] / 1000);
> >         max_freq = (bus->devfreq->profile->freq_table[max_state - 1] / 1000);
> > --
> > 2.17.1
> >
>
>
> --
> Best Regards,
> Chanwoo Choi



-- 
Best Regards,
Chanwoo Choi