Re: [PATCH v5 3/4] clk: samsung: exynos5433: Add runtime PM support

[Ulf Hansson <ulf.hansson@linaro.org>]

On 25 January 2017 at 12:53, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> Add runtime pm support for all clock controller units (CMU), which belongs
> to power domains and require special handling during on/off operations.
> Typically special values has to be written to MUX registers to change
> internal clocks parents to OSC clock before turning power off. During such
> operation all clocks, which enters CMU has to be enabled to let MUX to
> stabilize. Also for each CMU there is one special parent clock, which has
> to be enabled all the time when any access to CMU registers is done.
>
> This patch solves most of the mysterious external abort and freeze issues
> caused by a lack of proper parent CMU clock enabled or incorrect turn off
> procedure.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---

[...]

> --- a/drivers/clk/samsung/clk-exynos5433.c
> +++ b/drivers/clk/samsung/clk-exynos5433.c
> @@ -9,9 +9,14 @@
>   * Common Clock Framework support for Exynos5443 SoC.
>   */
>
> +#include <linux/clk.h>
>  #include <linux/clk-provider.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/slab.h>
>
>  #include <dt-bindings/clock/exynos5433.h>
>

[...]

> +struct exynos5433_cmu_data {
> +       struct samsung_clk_provider ctx;
> +
> +       struct samsung_clk_reg_dump *clk_save;
> +       unsigned int nr_clk_save;
> +       const struct samsung_clk_reg_dump *clk_suspend;
> +       unsigned int nr_clk_suspend;
> +
> +       struct clk *clk;
> +       struct clk **pclks;
> +       int nr_pclks;
> +};
> +
> +static int exynos5433_cmu_suspend(struct device *dev)
> +{
> +       struct exynos5433_cmu_data *data = dev_get_drvdata(dev);
> +       int i;
> +
> +       samsung_clk_save(data->ctx.reg_base, data->clk_save,
> +                        data->nr_clk_save);
> +
> +       for (i = 0; i < data->nr_pclks; i++)
> +               clk_enable(data->pclks[i]);
> +
> +       samsung_clk_restore(data->ctx.reg_base, data->clk_suspend,
> +                           data->nr_clk_suspend);
> +
> +       for (i = 0; i < data->nr_pclks; i++)
> +               clk_disable(data->pclks[i]);
> +
> +       clk_disable(data->clk);
> +
> +       return 0;
> +}
> +
> +static int exynos5433_cmu_resume(struct device *dev)
> +{
> +       struct exynos5433_cmu_data *data = dev_get_drvdata(dev);
> +       int i;
> +
> +       clk_enable(data->clk);
> +
> +       for (i = 0; i < data->nr_pclks; i++)
> +               clk_enable(data->pclks[i]);
> +
> +       samsung_clk_restore(data->ctx.reg_base, data->clk_save,
> +                           data->nr_clk_save);
> +
> +       for (i = 0; i < data->nr_pclks; i++)
> +               clk_disable(data->pclks[i]);
> +
> +       return 0;
> +}
> +
> +static int __init exynos5433_cmu_probe(struct platform_device *pdev)
> +{
> +       const struct samsung_cmu_info *info;
> +       struct exynos5433_cmu_data *data;
> +       struct samsung_clk_provider *ctx;
> +       struct device *dev = &pdev->dev;
> +       struct resource *res;
> +       void __iomem *reg_base;
> +       struct clk **clk_table;
> +       int i;
> +
> +       info = of_device_get_match_data(dev);
> +
> +       data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +       if (!data)
> +               return -ENOMEM;
> +       ctx = &data->ctx;
> +
> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +       reg_base = devm_ioremap_resource(dev, res);
> +       if (!reg_base) {
> +               dev_err(dev, "failed to map registers\n");
> +               return -ENOMEM;
> +       }
> +
> +       clk_table = devm_kcalloc(dev, info->nr_clk_ids, sizeof(struct clk *),
> +                                GFP_KERNEL);
> +       if (!clk_table)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < info->nr_clk_ids; ++i)
> +               clk_table[i] = ERR_PTR(-ENOENT);
> +
> +       ctx->clk_data.clks = clk_table;
> +       ctx->clk_data.clk_num = info->nr_clk_ids;
> +       ctx->reg_base = reg_base;
> +       ctx->dev = dev;
> +       spin_lock_init(&ctx->lock);
> +
> +       data->clk_save = samsung_clk_alloc_reg_dump(info->clk_regs,
> +                                                   info->nr_clk_regs);
> +       data->nr_clk_save = info->nr_clk_regs;
> +       data->clk_suspend = info->suspend_regs;
> +       data->nr_clk_suspend = info->nr_suspend_regs;
> +       data->nr_pclks = of_count_phandle_with_args(dev->of_node, "clocks",
> +                                                   "#clock-cells");
> +       if (data->nr_pclks > 0) {
> +               data->pclks = devm_kcalloc(dev, sizeof(struct clk *),
> +                                          data->nr_pclks, GFP_KERNEL);
> +
> +               for (i = 0; i < data->nr_pclks; i++) {
> +                       struct clk *clk = of_clk_get(dev->of_node, i);
> +
> +                       if (IS_ERR(clk))
> +                               return PTR_ERR(clk);
> +                       data->pclks[i] = clk;
> +               }
> +       }
> +
> +       /*
> +        * Prepare all parent clocks here to avoid potential deadlock caused
> +        * by global clock "prepare lock" grabbed by runtime pm callbacks
> +        * from pm workers.
> +        */

I don't understand why this potentially could cause a deadlock. Can
you please elaborate.

To me, I think you should be fine doing clk_prepare_enable() and
clk_disable_unprepare() from exynos5433_cmu_suspend|resume(), but I
may be missing something.

> +       for (i = 0; i < data->nr_pclks; i++)
> +               clk_prepare(data->pclks[i]);
> +
> +       if (info->clk_name)
> +               data->clk = clk_get(dev, info->clk_name);
> +       clk_prepare_enable(data->clk);
> +
> +       platform_set_drvdata(pdev, data);
> +
> +       /*
> +        * Enable runtime pm here, so clock core with use runtime pm for all
> +        * registered clocks. Additionally call pm_runtime_get_sync to ensure
> +        * that clock core will not runtime suspend our clock controller in
> +        * the middle of clock registration (clock core might call runtime pm
> +        * on newly registered clocks, for example to recalculate clock rate).
> +        */

Instead of the rather confusing comment about the call to
pm_runtime_get_sync(), let's instead state that we increase the
runtime PM usage count during the clock registration, to avoid the
clock core from runtime suspending the device.

In other words, before calling pm_runtime_set_active(), add a call
pm_runtime_get_noresume() and then remove the latter call to
pm_runtime_get_sync().

> +       pm_runtime_set_active(dev);
> +       pm_runtime_enable(dev);
> +       pm_runtime_get_sync(dev);
> +
> +       if (info->pll_clks)
> +               samsung_clk_register_pll(ctx, info->pll_clks, info->nr_pll_clks,
> +                                        reg_base);
> +       if (info->mux_clks)
> +               samsung_clk_register_mux(ctx, info->mux_clks,
> +                                        info->nr_mux_clks);
> +       if (info->div_clks)
> +               samsung_clk_register_div(ctx, info->div_clks,
> +                                        info->nr_div_clks);
> +       if (info->gate_clks)
> +               samsung_clk_register_gate(ctx, info->gate_clks,
> +                                         info->nr_gate_clks);
> +       if (info->fixed_clks)
> +               samsung_clk_register_fixed_rate(ctx, info->fixed_clks,
> +                                               info->nr_fixed_clks);
> +       if (info->fixed_factor_clks)
> +               samsung_clk_register_fixed_factor(ctx, info->fixed_factor_clks,
> +                                                 info->nr_fixed_factor_clks);
> +
> +       samsung_clk_of_add_provider(dev->of_node, ctx);
> +       pm_runtime_put(dev);
> +
> +       return 0;
> +}
>

[...]

Kind regards
Uffe