[RFC 1/3] clk: inherit display clocks enabled by bootloader

[Rajendra Nayak]

Hi Rob,

On 07/11/2017 11:50 PM, Rob Clark wrote:
> The goal here is to support inheriting a display setup by bootloader,
> although there may also be some non-display related use-cases.
> 
> Rough idea is to add a flag for clks and power domains that might
> already be enabled when kernel starts, and make corresponding fixups
> to clk enable/prepare_count and power-domain state so that these are
> not automatically disabled late in boot.
> 
> If bootloader is enabling display, and kernel is using efifb before
> real display driver is loaded (potentially from kernel module after
> userspace starts, in a typical distro kernel), we don't want to kill
> the clocks and power domains that are used by the display before
> userspace starts.
> 
> Second part is for drm/msm to check if display related clocks are
> enabled when it is loaded, and if so read back hw state to sync
> existing display state w/ software state, and skip the initial
> clk_enable's and otherwise fixing up clk/regulator/etc ref counts
> (skipping the normal display-enable codepaths), therefore inheriting
> the enable done by bootloader.
> 
> Obviously this should be split up into multiple patches and many
> TODOs addressed.  But I guess this is enough for now to start
> discussing the approach, and in particular how drm and clock/pd
> drivers work together to handle handover from bootloader.
> 
> The CLK_INHERIT_BOOTLOADER and related gsdc flag should only be set
> on leaf nodes.
> ---

[]..

> diff --git a/drivers/clk/qcom/common.c b/drivers/clk/qcom/common.c
> index d523991c945f..90b698c910d0 100644
> --- a/drivers/clk/qcom/common.c
> +++ b/drivers/clk/qcom/common.c
> @@ -11,6 +11,7 @@
>   * GNU General Public License for more details.
>   */
>  
> +#include <linux/clk.h>
>  #include <linux/export.h>
>  #include <linux/module.h>
>  #include <linux/regmap.h>
> @@ -258,6 +259,33 @@ int qcom_cc_really_probe(struct platform_device *pdev,
>  	if (ret)
>  		return ret;
>  
> +	/* Check which of clocks that we inherit state from bootloader
> +	 * are enabled, and fixup enable/prepare state (as well as that
> +	 * of it's parents).
> +	 *
> +	 * TODO can we assume that parents coming from another clk
> +	 * driver are already registered?
> +	 */
> +	for (i = 0; i < num_clks; i++) {
> +		struct clk_hw *hw;
> +
> +		if (!rclks[i])
> +			continue;
> +
> +		hw = &rclks[i]->hw;
> +
> +		if (!(hw->init->flags & CLK_INHERIT_BOOTLOADER))
> +			continue;
> +
> +		if (!clk_is_enabled_regmap(hw))
> +			continue;
> +
> +		dev_dbg(dev, "%s is enabled from bootloader!\n",
> +			  hw->init->name);
> +
> +		clk_inherit_enabled(hw->clk);

how about just calling a clk_prepare_enable(hw->clk) instead of adding a new API?
The flag could also be something qcom specific and then we avoid having to add
anything in generic CCF code and its all handled in the qcom clock drivers.

> +	}
> +
>  	reset = &cc->reset;
>  	reset->rcdev.of_node = dev->of_node;
>  	reset->rcdev.ops = &qcom_reset_ops;

[] ..

> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
> index a4f3580587b7..440d819b2d9d 100644
> --- a/drivers/clk/qcom/gdsc.c
> +++ b/drivers/clk/qcom/gdsc.c
> @@ -291,6 +291,12 @@ static int gdsc_init(struct gdsc *sc)
>  	if ((sc->flags & VOTABLE) && on)
>  		gdsc_enable(&sc->pd);
>  
> +	if ((sc->flags & INHERIT_BL) && on) {
> +		pr_debug("gdsc: %s is enabled from bootloader!\n", sc->pd.name);
> +		gdsc_enable(&sc->pd);
> +		sc->pd.flags |= GENPD_FLAG_ALWAYS_ON;

Would this not prevent the powerdomain from ever getting disabled?

regards,
Rajendra

> +	}
> +
>  	if (on || (sc->pwrsts & PWRSTS_RET))
>  		gdsc_force_mem_on(sc);
>  	else
> diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
> index 39648348e5ec..3b5e64b060c2 100644
> --- a/drivers/clk/qcom/gdsc.h
> +++ b/drivers/clk/qcom/gdsc.h
> @@ -53,6 +53,7 @@ struct gdsc {
>  #define VOTABLE		BIT(0)
>  #define CLAMP_IO	BIT(1)
>  #define HW_CTRL		BIT(2)
> +#define INHERIT_BL	BIT(3)
>  	struct reset_controller_dev	*rcdev;
>  	unsigned int			*resets;
>  	unsigned int			reset_count;
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index c59c62571e4f..4d5505f92329 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -35,6 +35,7 @@
>  #define CLK_IS_CRITICAL		BIT(11) /* do not gate, ever */
>  /* parents need enable during gate/ungate, set rate and re-parent */
>  #define CLK_OPS_PARENT_ENABLE	BIT(12)
> +#define CLK_INHERIT_BOOTLOADER	BIT(13) /* clk may be enabled from bootloader */
>  
>  struct clk;
>  struct clk_hw;
> diff --git a/include/linux/clk.h b/include/linux/clk.h
> index 91bd464f4c9b..461991fc57e2 100644
> --- a/include/linux/clk.h
> +++ b/include/linux/clk.h
> @@ -391,6 +391,15 @@ void clk_disable(struct clk *clk);
>  void clk_bulk_disable(int num_clks, const struct clk_bulk_data *clks);
>  
>  /**
> + * clk_inherit_enabled - update the enable/prepare count of a clock and it's
> + * parents for clock enabled by bootloader.
> + *
> + * Intended to be used by clock drivers to inform the clk core of a clock
> + * that is already running.
> + */
> +void clk_inherit_enabled(struct clk *clk);
> +
> +/**
>   * clk_get_rate - obtain the current clock rate (in Hz) for a clock source.
>   *		  This is only valid once the clock source has been enabled.
>   * @clk: clock source
> 

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