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    SubjectRe: [RFC PATCH v3 5/7] devfreq: exynos-bus: Add interconnect functionality to exynos-bus
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    Hi Artur,

    On 1/24/20 13:22, Artur Świgoń wrote:
    > Hi Georgi,
    >
    > On Wed, 2020-01-22 at 19:02 +0200, Georgi Djakov wrote:
    >> Hi Artur,
    >>
    >> On 12/20/19 13:56, Artur Świgoń 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
    >>
    >> Just to note that usually the provider consists of multiple nodes and each node
    >> represents a single master or slave port on the AXI bus for example. I am not
    >> sure whether this represents correctly the Exynos hardware, so it's up to
    >> you.
    >>
    >>> runtime, in probing order (subject to the above-mentioned exception
    >>> regarding relative order). This approach allows for using this driver with
    >>> various Exynos SoCs.
    >>
    >> This sounds good. I am wondering whether such dynamic probing would be useful
    >> for other platforms too. Then maybe it would make sense to even have a common DT
    >> property, but we will see.
    >>
    >> Is this going to be used only together with devfreq?
    >
    > Yes, this functions solely as an extension to devfreq, hence the slightly
    > unusual architecture (one icc_provider/icc_node per devfreq).

    Ok, thanks for clarifying.

    > (Compared to a singleton icc_provider, this approach yields less code with
    > a very simple xlate()).
    >
    > With exactly one icc_node for every devfreq device, I think I will actually
    > reuse the devfreq ID (as seen in the device name, e.g. the "3" in "devfreq3")
    > for the node ID. The devfreq framework already does the dynamic numbering
    > thing that I do in this patch using IDR.
    >

    Sounds good.

    >>> 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.
    >>
    >> How about the case where CONFIG_INTERCONNECT=m. Looks like the build will fail
    >> if CONFIG_ARM_EXYNOS_BUS_DEVFREQ=y, so this dependency should be expressed in
    >> Kconfig.
    >
    > I think adding:
    > depends on INTERCONNECT || !INTERCONNECT

    Yes, exactly.

    > under ARM_EXYNOS_BUS_DEVFREQ does the trick.
    >
    >>>
    >>> Signed-off-by: Artur Świgoń <a.swigon@samsung.com>
    >>> ---
    >>> 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");
    >>> + 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");
    >>> + 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 */
    >>> +
    >>> + 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);
    >>> +
    >>> + parent_node = exynos_bus_icc_get_parent(bus);
    >>> + if (IS_ERR(parent_node)) {
    >>> + ret = PTR_ERR(parent_node);
    >>> + goto err_parent;
    >>> + }
    >>> +
    >>> + 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);
    >>> + 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) {

    I have been also thinking that all the code that you add in this patch would fit
    nicely into a separate interconnect provider driver. Then instead of the above
    icc_init() you can create a sub-device (platform_device_register_data() maybe?).
    The separate driver will be handling just the interconnect functionality and
    could be enabled on top of this devfreq driver.

    Thanks,
    Georgi

    P.S. I think that grouping all the related patches into a single patch-set would
    make reviewing them easier. Then we can decide about the merge path of each.

    >>> + 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);
    >>>
    >>
    >>

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