linux-kernel - Re: [PATCH 2/2] PM / clk: Add support for obtaining clocks from device-tree

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Date:	Mon, 7 Mar 2016 09:48:25 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH 2/2] PM / clk: Add support for obtaining clocks from device-tree

Hi Jon,

On Fri, Mar 4, 2016 at 4:33 PM, Jon Hunter <jonathanh@...dia.com> wrote:
> The PM clocks framework requires clients to pass either a con-id or a
> valid clk pointer in order to add a clock to a device. Add a new
> function pm_clk_add_clks_of() to allows device clocks to be retrieved
> from device-tree and populated for a given device. Note that there
> should be no need to add a stub function for this new function when
> CONFIG_OF is not selected because the OF functions used already have
> stubs functions.
>
> In order to handle errors encountered when adding clocks from
> device-tree, add a function pm_clk_remove_clk() to remove any clocks
> (using a pointer to the clk structure) that have been added
> successfully before the error occurred.
>
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> ---
>  drivers/base/power/clock_ops.c | 85 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_clock.h       |  9 +++++
>  2 files changed, 94 insertions(+)
>
> diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
> index 272a52ebafc0..5aa7365699c1 100644
> --- a/drivers/base/power/clock_ops.c
> +++ b/drivers/base/power/clock_ops.c
> @@ -138,6 +138,58 @@ int pm_clk_add_clk(struct device *dev, struct clk *clk)
>  }
>
>  /**
> + * pm_clk_add_clks_of - Start using device clock(s) for power management.
> + * @dev: Device whose clock(s) is going to be used for power management.
> + *
> + * Add a series of clocks described in the 'clocks' device-tree node for
> + * a device to the list of clocks used for the power management of @dev.

This adds all clocks referenced by the device node, while not all clocks may
be suitable for power management, and some of them may be under explicit
driver control.
Cfr. drivers/clk/shmobile/renesas-cpg-mssr.c:cpg_mssr_attach_dev(), which
looks for module clocks, or core clocks explicitly listed in core_pm_clks[].

What about adding an optional filter function to filter for suitable clocks?

> + */
> +int pm_clk_add_clks_of(struct device *dev)
> +{
> +       struct clk **clks;
> +       unsigned int i, count;
> +       int ret;
> +
> +       if (!dev || !dev->of_node)
> +               return -EINVAL;
> +
> +       count = of_count_phandle_with_args(dev->of_node, "clocks",
> +                                          "#clock-cells");
> +       if (count == 0)
> +               return -ENODEV;
> +
> +       clks = kcalloc(count, sizeof(*clks), GFP_KERNEL);
> +       if (!clks)
> +               return -ENOMEM;
> +

Don't you have to call pm_clk_create() here, to allocate a pm_subsys_data
structure that pm_clk_add_clk() can populate?

> +       for (i = 0; i < count; i++) {
> +               clks[i] = of_clk_get(dev->of_node, i);
> +               if (IS_ERR(clks[i])) {
> +                       ret = PTR_ERR(clks[i]);
> +                       goto error;
> +               }
> +
> +               ret = pm_clk_add_clk(dev, clks[i]);
> +               if (ret) {
> +                       clk_put(clks[i]);
> +                       goto error;
> +               }
> +       }
> +
> +       kfree(clks);
> +
> +       return 0;
> +
> +error:
> +       while (i--)
> +               pm_clk_remove_clk(dev, clks[i]);

Just pm_clk_destroy(dev) to destroy all at once?

> +
> +       kfree(clks);
> +
> +       return ret;
> +}

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds