Re: [PATCH v11 04/10] memory: tegra124-emc: Make driver modular

[Thierry Reding]

On Thu, Dec 03, 2020 at 10:24:33PM +0300, Dmitry Osipenko wrote:
> Add modularization support to the Tegra124 EMC driver, which now can be
> compiled as a loadable kernel module.
> 
> Note that EMC clock must be registered at clk-init time, otherwise PLLM
> will be disabled as unused clock at boot time if EMC driver is compiled
> as a module. Hence add a prepare/complete callbacks. similarly to what is
> done for the Tegra20/30 EMC drivers.
> 
> Tested-by: Nicolas Chauvet <kwizart@xxxxxxxxx>
> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> ---
>  drivers/clk/tegra/Kconfig            |  3 ++
>  drivers/clk/tegra/Makefile           |  2 +-
>  drivers/clk/tegra/clk-tegra124-emc.c | 41 ++++++++++++++++++++++++----
>  drivers/clk/tegra/clk-tegra124.c     | 26 ++++++++++++++++--
>  drivers/clk/tegra/clk.h              | 18 ++++++++----
>  drivers/memory/tegra/Kconfig         |  3 +-
>  drivers/memory/tegra/tegra124-emc.c  | 31 ++++++++++++++-------
>  include/linux/clk/tegra.h            |  8 ++++++
>  include/soc/tegra/emc.h              | 16 -----------
>  9 files changed, 106 insertions(+), 42 deletions(-)
>  delete mode 100644 include/soc/tegra/emc.h
> 
> diff --git a/drivers/clk/tegra/Kconfig b/drivers/clk/tegra/Kconfig
> index deaa4605824c..90df619dc087 100644
> --- a/drivers/clk/tegra/Kconfig
> +++ b/drivers/clk/tegra/Kconfig
> @@ -7,3 +7,6 @@ config TEGRA_CLK_DFLL
>  	depends on ARCH_TEGRA_124_SOC || ARCH_TEGRA_210_SOC
>  	select PM_OPP
>  	def_bool y
> +
> +config TEGRA124_CLK_EMC
> +	bool
> diff --git a/drivers/clk/tegra/Makefile b/drivers/clk/tegra/Makefile
> index eec2313fd37e..7b1816856eb5 100644
> --- a/drivers/clk/tegra/Makefile
> +++ b/drivers/clk/tegra/Makefile
> @@ -22,7 +22,7 @@ obj-$(CONFIG_ARCH_TEGRA_3x_SOC)		+= clk-tegra20-emc.o
>  obj-$(CONFIG_ARCH_TEGRA_114_SOC)	+= clk-tegra114.o
>  obj-$(CONFIG_ARCH_TEGRA_124_SOC)	+= clk-tegra124.o
>  obj-$(CONFIG_TEGRA_CLK_DFLL)		+= clk-tegra124-dfll-fcpu.o
> -obj-$(CONFIG_TEGRA124_EMC)		+= clk-tegra124-emc.o
> +obj-$(CONFIG_TEGRA124_CLK_EMC)		+= clk-tegra124-emc.o
>  obj-$(CONFIG_ARCH_TEGRA_132_SOC)	+= clk-tegra124.o
>  obj-y					+= cvb.o
>  obj-$(CONFIG_ARCH_TEGRA_210_SOC)	+= clk-tegra210.o
> diff --git a/drivers/clk/tegra/clk-tegra124-emc.c b/drivers/clk/tegra/clk-tegra124-emc.c
> index 745f9faa98d8..bdf6f4a51617 100644
> --- a/drivers/clk/tegra/clk-tegra124-emc.c
> +++ b/drivers/clk/tegra/clk-tegra124-emc.c
> @@ -11,7 +11,9 @@
>  #include <linux/clk-provider.h>
>  #include <linux/clk.h>
>  #include <linux/clkdev.h>
> +#include <linux/clk/tegra.h>
>  #include <linux/delay.h>
> +#include <linux/export.h>
>  #include <linux/io.h>
>  #include <linux/module.h>
>  #include <linux/of_address.h>
> @@ -21,7 +23,6 @@
>  #include <linux/string.h>
>  
>  #include <soc/tegra/fuse.h>
> -#include <soc/tegra/emc.h>
>  
>  #include "clk.h"
>  
> @@ -80,6 +81,9 @@ struct tegra_clk_emc {
>  	int num_timings;
>  	struct emc_timing *timings;
>  	spinlock_t *lock;
> +
> +	tegra124_emc_prepare_timing_change_cb *prepare_timing_change;
> +	tegra124_emc_complete_timing_change_cb *complete_timing_change;
>  };
>  
>  /* Common clock framework callback implementations */
> @@ -176,6 +180,9 @@ static struct tegra_emc *emc_ensure_emc_driver(struct tegra_clk_emc *tegra)
>  	if (tegra->emc)
>  		return tegra->emc;
>  
> +	if (!tegra->prepare_timing_change || !tegra->complete_timing_change)
> +		return NULL;
> +
>  	if (!tegra->emc_node)
>  		return NULL;
>  
> @@ -241,7 +248,7 @@ static int emc_set_timing(struct tegra_clk_emc *tegra,
>  
>  	div = timing->parent_rate / (timing->rate / 2) - 2;
>  
> -	err = tegra_emc_prepare_timing_change(emc, timing->rate);
> +	err = tegra->prepare_timing_change(emc, timing->rate);
>  	if (err)
>  		return err;
>  
> @@ -259,7 +266,7 @@ static int emc_set_timing(struct tegra_clk_emc *tegra,
>  
>  	spin_unlock_irqrestore(tegra->lock, flags);
>  
> -	tegra_emc_complete_timing_change(emc, timing->rate);
> +	tegra->complete_timing_change(emc, timing->rate);
>  
>  	clk_hw_reparent(&tegra->hw, __clk_get_hw(timing->parent));
>  	clk_disable_unprepare(tegra->prev_parent);
> @@ -473,8 +480,8 @@ static const struct clk_ops tegra_clk_emc_ops = {
>  	.get_parent = emc_get_parent,
>  };
>  
> -struct clk *tegra_clk_register_emc(void __iomem *base, struct device_node *np,
> -				   spinlock_t *lock)
> +struct clk *tegra124_clk_register_emc(void __iomem *base, struct device_node *np,
> +				      spinlock_t *lock)
>  {
>  	struct tegra_clk_emc *tegra;
>  	struct clk_init_data init;
> @@ -538,3 +545,27 @@ struct clk *tegra_clk_register_emc(void __iomem *base, struct device_node *np,
>  
>  	return clk;
>  };
> +
> +void tegra124_clk_set_emc_callbacks(tegra124_emc_prepare_timing_change_cb *prep_cb,
> +				    tegra124_emc_complete_timing_change_cb *complete_cb)
> +{
> +	struct clk *clk = __clk_lookup("emc");
> +	struct tegra_clk_emc *tegra;
> +	struct clk_hw *hw;
> +
> +	if (clk) {
> +		hw = __clk_get_hw(clk);
> +		tegra = container_of(hw, struct tegra_clk_emc, hw);
> +
> +		tegra->prepare_timing_change = prep_cb;
> +		tegra->complete_timing_change = complete_cb;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(tegra124_clk_set_emc_callbacks);
> +
> +bool tegra124_clk_emc_driver_available(struct clk_hw *hw)
> +{
> +	struct tegra_clk_emc *tegra = container_of(hw, struct tegra_clk_emc, hw);
> +
> +	return tegra->prepare_timing_change && tegra->complete_timing_change;
> +}

This looks a bit hackish and I prefer the way this was done for
Tegra210. But that's mostly an implementation detail and we can always
restructure this if we want to.

> diff --git a/drivers/clk/tegra/clk-tegra124.c b/drivers/clk/tegra/clk-tegra124.c
> index e931319dcc9d..934520aab6e3 100644
> --- a/drivers/clk/tegra/clk-tegra124.c
> +++ b/drivers/clk/tegra/clk-tegra124.c
> @@ -1500,6 +1500,26 @@ static void __init tegra124_132_clock_init_pre(struct device_node *np)
>  	writel(plld_base, clk_base + PLLD_BASE);
>  }
>  
> +static struct clk *tegra124_clk_src_onecell_get(struct of_phandle_args *clkspec,
> +						void *data)
> +{
> +	struct clk_hw *hw;
> +	struct clk *clk;
> +
> +	clk = of_clk_src_onecell_get(clkspec, data);
> +	if (IS_ERR(clk))
> +		return clk;
> +
> +	hw = __clk_get_hw(clk);
> +
> +	if (clkspec->args[0] == TEGRA124_CLK_EMC) {
> +		if (!tegra124_clk_emc_driver_available(hw))
> +			return ERR_PTR(-EPROBE_DEFER);
> +	}
> +
> +	return clk;
> +}

Hm... why exactly do we need this? On Tegra210 and later, the EMC driver
is the only consumer of the EMC clock and since it also provides some of
the necessary parts to scale the EMC clock, that's a chicken and egg
problem. I'm not sure I fully understand how this is supposed to work
here and why we can't do this in a similar way than Tegra210.

Thierry

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