Re: [PATCH v7 2/6] interconnect: Add generic interconnect driver for Exynos SoCs

[Chanwoo Choi]

Hi Sylwester,

On Tue, Nov 3, 2020 at 8:32 PM Sylwester Nawrocki
<s.nawrocki@xxxxxxxxxxx> wrote:
>
> On 03.11.2020 10:37, Chanwoo Choi wrote:
> > On 10/30/20 9:51 PM, Sylwester Nawrocki wrote:
> >> This patch adds a generic interconnect driver for Exynos SoCs in order
> >> to provide interconnect functionality for each "samsung,exynos-bus"
> >> compatible device.
> >>
> >> The SoC topology is a graph (or more specifically, a tree) and its
> >> edges are specified using the 'samsung,interconnect-parent' in the
> >
> > samsung,interconnect-parent -> interconnects?
>
> Yes, I will rephrase the whole commit message as it's a bit outdated now.
>
> I've changed the sentence to:
> "The SoC topology is a graph (or more specifically, a tree) and its
> edges are described by specifying in the 'interconnects' property
> the interconnect consumer path for each interconnect provider DT node."
>
> >> 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 dynamically at runtime. 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.
> >>
> >> The bus-width DT property is to determine the interconnect data
> >> width and traslate requested bandwidth to clock frequency for each
> >> bus.
> >>
> >> Signed-off-by: Artur Świgoń <a.swigon@xxxxxxxxxxx>
> >> Signed-off-by: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx>
>
> >> +++ b/drivers/interconnect/exynos/exynos.c
>
> >> +struct exynos_icc_priv {
> >> +    struct device *dev;
> >> +
> >> +    /* One interconnect node per provider */
> >> +    struct icc_provider provider;
> >> +    struct icc_node *node;
> >> +
> >> +    struct dev_pm_qos_request qos_req;
> >> +    u32 bus_clk_ratio;
> >> +};
> >> +
> >> +static struct icc_node *exynos_icc_get_parent(struct device_node *np)
> >> +{
> >> +    struct of_phandle_args args;
> >> +    struct icc_node_data *icc_node_data;
> >> +    struct icc_node *icc_node;
> >> +    int num, ret;
> >> +
> >> +    num = of_count_phandle_with_args(np, "interconnects",
> >> +                                     "#interconnect-cells");
> >> +    if (num < 1)
> >> +            return NULL; /* parent nodes are optional */
> >> +
> >> +    /* Get the interconnect target node */
> >> +    ret = of_parse_phandle_with_args(np, "interconnects",
> >> +                                    "#interconnect-cells", 0, &args);
> >> +    if (ret < 0)
> >> +            return ERR_PTR(ret);
> >> +
> >> +    icc_node_data = of_icc_get_from_provider(&args);
> >> +    of_node_put(args.np);
> >> +
> >> +    if (IS_ERR(icc_node_data))
> >> +            return ERR_CAST(icc_node_data);
> >> +
> >> +    icc_node = icc_node_data->node;
> >> +    kfree(icc_node_data);
> >> +
> >> +    return icc_node;
> >> +}
> >
> > I have a question about exynos_icc_get_parent().
> > As I checked, this function returns the only one icc_node
> > as parent node. But, bus_display dt node in the exynos4412.dtsi
> > specifies the two interconnect node as following with bus_leftbus, bus_dmc,
> >
> > When I checked the return value of exynos_icc_get_parent()
> > during probing for bus_display device, exynos_icc_get_parent() function
> > only returns 'bus_leftbus' icc_node. Do you need to add two phandle
> > of icc node?
>
> Yes, as we use the interconnect consumer bindings we need to specify a path,
> i.e. a <initiator, target> pair. When the provider node initializes it will
> link itself to that path. Currently the provider driver uses just the first
> phandle.

As I knew, the interconnect consumer bindings use the two phandles
in the interconnect core as you commented. But, in case of this,
even if add two phandles with interconnect consumding binding style,
the exynos interconnect driver only uses the first phandle.

Instead, I think we better explain this case into a dt-binding
document for users.

> > +++ b/arch/arm/boot/dts/exynos4412.dtsi
> > @@ -472,7 +472,7 @@
> >                         clocks = <&clock CLK_ACLK160>;
> >                         clock-names = "bus";
> >                         operating-points-v2 = <&bus_display_opp_table>;
> >                         interconnects = <&bus_leftbus &bus_dmc>;
> >                         #interconnect-cells = <0>;
> >                         status = "disabled";
> >                 };
>
> --
> Regards,
> Sylwester
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-- 
Best Regards,
Chanwoo Choi