linux-kernel - Re: [RFC v6 net-next 5/9] mfd: add interface to check whether a device is mfd

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Date:   Mon, 31 Jan 2022 08:47:33 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Colin Foster <colin.foster@...advantage.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>, UNGLinuxDriver@...rochip.com,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        katie.morris@...advantage.com
Subject: Re: [RFC v6 net-next 5/9] mfd: add interface to check whether a
 device is mfd

On Sat, 29 Jan 2022, Colin Foster wrote:

> Some drivers will need to create regmaps differently based on whether they
> are a child of an MFD or a standalone device. An example of this would be
> if a regmap were directly memory-mapped or an external bus. In the
> memory-mapped case a call to devm_regmap_init_mmio would return the correct
> regmap. In the case of an MFD, the regmap would need to be requested from
> the parent device.
> 
> This addition allows the driver to correctly reason about these scenarios.
> 
> Signed-off-by: Colin Foster <colin.foster@...advantage.com>
> ---
>  drivers/mfd/mfd-core.c   |  6 ++++++
>  include/linux/mfd/core.h | 10 ++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index 684a011a6396..2ba6a692499b 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -33,6 +33,12 @@ static struct device_type mfd_dev_type = {
>  	.name	= "mfd_device",
>  };
>  
> +int device_is_mfd(struct platform_device *pdev)
> +{
> +	return (!strcmp(pdev->dev.type->name, mfd_dev_type.name));
> +}
> +EXPORT_SYMBOL(device_is_mfd);

As I said before, I really don't want MFDness leaking out into other
parts of the kernel.  Please find another way to differentiate between
devices registered via the MFD API and by other means.

I'm happy to help here.

How else could these devices be enumerated? 

>  int mfd_cell_enable(struct platform_device *pdev)
>  {
>  	const struct mfd_cell *cell = mfd_get_cell(pdev);
> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
> index 0bc7cba798a3..c0719436b652 100644
> --- a/include/linux/mfd/core.h
> +++ b/include/linux/mfd/core.h
> @@ -10,6 +10,7 @@
>  #ifndef MFD_CORE_H
>  #define MFD_CORE_H
>  
> +#include <generated/autoconf.h>
>  #include <linux/platform_device.h>
>  
>  #define MFD_RES_SIZE(arr) (sizeof(arr) / sizeof(struct resource))
> @@ -123,6 +124,15 @@ struct mfd_cell {
>  	int			num_parent_supplies;
>  };
>  
> +#ifdef CONFIG_MFD_CORE
> +int device_is_mfd(struct platform_device *pdev);
> +#else
> +static inline int device_is_mfd(struct platform_device *pdev)
> +{
> +	return 0;
> +}
> +#endif
> +
>  /*
>   * Convenience functions for clients using shared cells.  Refcounting
>   * happens automatically, with the cell's enable/disable callbacks

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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