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Date:   Mon, 21 Oct 2019 13:33:53 +0100
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Lee Jones <lee.jones@linaro.org>
Cc:     arnd@arndb.de, broonie@kernel.org, linus.walleij@linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        baohua@kernel.org, stephan@gerhold.net
Subject: Re: [PATCH v2 8/9] mfd: mfd-core: Remove usage counting for
 .{en,dis}able() call-backs
Message-ID: <20191021123353.nhb2ynq6d52skoif@holly.lan>
References: <20191021105822.20271-1-lee.jones@linaro.org>
 <20191021105822.20271-9-lee.jones@linaro.org>
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On Mon, Oct 21, 2019 at 11:58:21AM +0100, Lee Jones wrote:
> The MFD implementation for reference counting was complex and unnecessary.
> There was only one bona fide user which has now been converted to handle
> the process in a different way. Any future resource protection, shared
> enablement functions should be handed by the parent device, rather than
> through the MFD subsystem API.
> 
> Signed-off-by: Lee Jones <lee.jones@linaro.org>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>

> ---
>  drivers/mfd/mfd-core.c   | 57 +++++++---------------------------------
>  include/linux/mfd/core.h |  2 --
>  2 files changed, 9 insertions(+), 50 deletions(-)
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index 90b43b44a15a..5d56015baeeb 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -26,53 +26,31 @@ static struct device_type mfd_dev_type = {
>  int mfd_cell_enable(struct platform_device *pdev)
>  {
>  	const struct mfd_cell *cell = mfd_get_cell(pdev);
> -	int err = 0;
>  
>  	if (!cell->enable) {
>  		dev_dbg(&pdev->dev, "No .enable() call-back registered\n");
>  		return 0;
>  	}
>  
> -	/* only call enable hook if the cell wasn't previously enabled */
> -	if (atomic_inc_return(cell->usage_count) == 1)
> -		err = cell->enable(pdev);
> -
> -	/* if the enable hook failed, decrement counter to allow retries */
> -	if (err)
> -		atomic_dec(cell->usage_count);
> -
> -	return err;
> +	return cell->enable(pdev);
>  }
>  EXPORT_SYMBOL(mfd_cell_enable);
>  
>  int mfd_cell_disable(struct platform_device *pdev)
>  {
>  	const struct mfd_cell *cell = mfd_get_cell(pdev);
> -	int err = 0;
>  
>  	if (!cell->enable) {
>  		dev_dbg(&pdev->dev, "No .disable() call-back registered\n");
>  		return 0;
>  	}
>  
> -	/* only disable if no other clients are using it */
> -	if (atomic_dec_return(cell->usage_count) == 0)
> -		err = cell->disable(pdev);
> -
> -	/* if the disable hook failed, increment to allow retries */
> -	if (err)
> -		atomic_inc(cell->usage_count);
> -
> -	/* sanity check; did someone call disable too many times? */
> -	WARN_ON(atomic_read(cell->usage_count) < 0);
> -
> -	return err;
> +	return cell->disable(pdev);
>  }
>  EXPORT_SYMBOL(mfd_cell_disable);
>  
>  static int mfd_platform_add_cell(struct platform_device *pdev,
> -				 const struct mfd_cell *cell,
> -				 atomic_t *usage_count)
> +				 const struct mfd_cell *cell)
>  {
>  	if (!cell)
>  		return 0;
> @@ -81,7 +59,6 @@ static int mfd_platform_add_cell(struct platform_device *pdev,
>  	if (!pdev->mfd_cell)
>  		return -ENOMEM;
>  
> -	pdev->mfd_cell->usage_count = usage_count;
>  	return 0;
>  }
>  
> @@ -144,7 +121,7 @@ static inline void mfd_acpi_add_device(const struct mfd_cell *cell,
>  #endif
>  
>  static int mfd_add_device(struct device *parent, int id,
> -			  const struct mfd_cell *cell, atomic_t *usage_count,
> +			  const struct mfd_cell *cell,
>  			  struct resource *mem_base,
>  			  int irq_base, struct irq_domain *domain)
>  {
> @@ -206,7 +183,7 @@ static int mfd_add_device(struct device *parent, int id,
>  			goto fail_alias;
>  	}
>  
> -	ret = mfd_platform_add_cell(pdev, cell, usage_count);
> +	ret = mfd_platform_add_cell(pdev, cell);
>  	if (ret)
>  		goto fail_alias;
>  
> @@ -296,16 +273,9 @@ int mfd_add_devices(struct device *parent, int id,
>  {
>  	int i;
>  	int ret;
> -	atomic_t *cnts;
> -
> -	/* initialize reference counting for all cells */
> -	cnts = kcalloc(n_devs, sizeof(*cnts), GFP_KERNEL);
> -	if (!cnts)
> -		return -ENOMEM;
>  
>  	for (i = 0; i < n_devs; i++) {
> -		atomic_set(&cnts[i], 0);
> -		ret = mfd_add_device(parent, id, cells + i, cnts + i, mem_base,
> +		ret = mfd_add_device(parent, id, cells + i, mem_base,
>  				     irq_base, domain);
>  		if (ret)
>  			goto fail;
> @@ -316,17 +286,15 @@ int mfd_add_devices(struct device *parent, int id,
>  fail:
>  	if (i)
>  		mfd_remove_devices(parent);
> -	else
> -		kfree(cnts);
> +
>  	return ret;
>  }
>  EXPORT_SYMBOL(mfd_add_devices);
>  
> -static int mfd_remove_devices_fn(struct device *dev, void *c)
> +static int mfd_remove_devices_fn(struct device *dev, void *data)
>  {
>  	struct platform_device *pdev;
>  	const struct mfd_cell *cell;
> -	atomic_t **usage_count = c;
>  
>  	if (dev->type != &mfd_dev_type)
>  		return 0;
> @@ -337,20 +305,13 @@ static int mfd_remove_devices_fn(struct device *dev, void *c)
>  	regulator_bulk_unregister_supply_alias(dev, cell->parent_supplies,
>  					       cell->num_parent_supplies);
>  
> -	/* find the base address of usage_count pointers (for freeing) */
> -	if (!*usage_count || (cell->usage_count < *usage_count))
> -		*usage_count = cell->usage_count;
> -
>  	platform_device_unregister(pdev);
>  	return 0;
>  }
>  
>  void mfd_remove_devices(struct device *parent)
>  {
> -	atomic_t *cnts = NULL;
> -
> -	device_for_each_child_reverse(parent, &cnts, mfd_remove_devices_fn);
> -	kfree(cnts);
> +	device_for_each_child_reverse(parent, NULL, mfd_remove_devices_fn);
>  }
>  EXPORT_SYMBOL(mfd_remove_devices);
>  
> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
> index bd8c0e089164..919f09fb07b7 100644
> --- a/include/linux/mfd/core.h
> +++ b/include/linux/mfd/core.h
> @@ -30,8 +30,6 @@ struct mfd_cell {
>  	const char		*name;
>  	int			id;
>  
> -	/* refcounting for multiple drivers to use a single cell */
> -	atomic_t		*usage_count;
>  	int			(*enable)(struct platform_device *dev);
>  	int			(*disable)(struct platform_device *dev);
>  
> -- 
> 2.17.1
>