Re: [PATCH 1/2] clk: qcom: add API to safely park RCG2 sources

[Stephen Boyd <sboyd@kernel.org>]

Quoting Dmitry Baryshkov (2021-12-07 18:22:09)
> Some of RCG2 clocks can become stuck during the boot process, when
> device drivers are enabling and disabling the RCG2's parent clocks.
> To prevernt such outcome of driver probe sequences, add API to park

s/prevernt/prevent/

> clocks to the safe clock source (typically TCXO).
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

I'd prefer this approach vs. adding a new clk flag. The clk framework
doesn't handle handoff properly today so we shouldn't try to bandage
that in the core.

> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index e1b1b426fae4..230b04a7427c 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -1036,6 +1036,40 @@ static void clk_rcg2_shared_disable(struct clk_hw *hw)
>         regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, cfg);
>  }
>  
> +int clk_rcg2_park_safely(struct regmap *regmap, u32 offset, unsigned int safe_src)

Please add kernel doc as it's an exported symbol.

> +{
> +       unsigned int val, ret, count;
> +
> +       ret = regmap_read(regmap, offset + CFG_REG, &val);
> +       if (ret)
> +               return ret;
> +
> +       /* assume safe source is 0 */

Are we assuming safe source is 0 here? It looks like we pass it in now?

> +       if ((val & CFG_SRC_SEL_MASK) == (safe_src << CFG_SRC_SEL_SHIFT))
> +               return 0;
> +
> +       regmap_write(regmap, offset + CFG_REG, safe_src << CFG_SRC_SEL_SHIFT);
> +
> +       ret = regmap_update_bits(regmap, offset + CMD_REG,
> +                                CMD_UPDATE, CMD_UPDATE);
> +       if (ret)
> +               return ret;
> +
> +       /* Wait for update to take effect */
> +       for (count = 500; count > 0; count--) {
> +               ret = regmap_read(regmap, offset + CMD_REG, &val);
> +               if (ret)
> +                       return ret;
> +               if (!(val & CMD_UPDATE))
> +                       return 0;
> +               udelay(1);
> +       }
> +
> +       WARN(1, "the rcg didn't update its configuration.");

Add a newline?

> +       return -EBUSY;
> +}
> +EXPORT_SYMBOL_GPL(clk_rcg2_park_safely);
> +