linux-kernel - Re: [PATCH v2] mfd: syscon: Decouple syscon interface from platform devices

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Message-ID: <6034841.GFrG3XCMdb@wuerfel>
Date:	Tue, 02 Sep 2014 17:20:03 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Pankaj Dubey <pankaj.dubey@...sung.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	lee.jones@...aro.org, kgene.kim@...sung.com,
	linux@....linux.org.uk, vikas.sajjan@...sung.com,
	joshi@...sung.com, naushad@...sung.com, thomas.ab@...sung.com,
	chow.kim@...sung.com, tomasz.figa@...il.com,
	Tomasz Figa <t.figa@...sung.com>,
	Alexander Shiyan <shc_work@...l.ru>,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH v2] mfd: syscon: Decouple syscon interface from platform devices

On Tuesday 02 September 2014 20:12:15 Pankaj Dubey wrote:
> Currently a syscon entity can only be registered directly through a
> platform device that binds to a dedicated syscon driver. However in
> certain cases it is required to bind a device with it's dedicated
> driver rather than binding with syscon driver.
> 
> For example, certain SoCs (e.g. Exynos) contain system controller
> blocks which perform various functions such as power domain control,
> CPU power management, low power mode control, but in addition contain
> certain IP integration glue, such as various signal masks,
> coprocessor power control, etc. In such case, there is a need to have
> a dedicated driver for such system controller but also share registers
> with other drivers. The latter is where the syscon interface is helpful.
> 
> This patch decouples syscon object from syscon platform driver, and
> allows to create syscon objects first time when it is required by
> calling of syscon_regmap_lookup_by APIs and keeps a list of such syscon
> objects along with syscon provider device_nodes and regmap handles.
> 
> Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> Signed-off-by: Tomasz Figa <t.figa@...sung.com>
> ---
> V1 of this patchset [1] and related discussion can be found here [1].
>  
> Changes since v1:
>  - Removed of_syscon_unregister function.
>  - Modified of_syscon_register function and it will be used by syscon.c 
>    to create syscon objects whenever required. 
>  - Removed platform device support from syscon.
>  - Removed syscon_regmap_lookup_by_pdevname API support.
>  - As there are significant changes w.r.t patchset v1, I am taking over
>    author for this patchset from Tomasz Figa.

Note that you got the Signed-off-by: list wrong, you should never have
any people listed as Signed-off-by after your own name, and they should
be listed before your name only when you are forwarding their patches.

> Note: Current kernel has clps711x user of syscon_regmap_lookup_by_pdevname and 
> will be broken after this patch. As per discussion over here [1], patches 
> for making these drivers DT based are ready and once that is done they can use
> syscon_regmap_lookup_by_phandle or syscon_regmap_lookup_by_compatible.
> 
> [1]: https://lkml.org/lkml/2014/8/22/81

Adding Alexander Shiyan to Cc here, so we can make sure this is well
coordinated.

I'm also adding Michal Simek, since here was involved in earlier discussions
about doing this.

>  drivers/mfd/syscon.c       |  143 +++++++++++++-------------------------------
>  include/linux/mfd/syscon.h |    1 +
>  2 files changed, 44 insertions(+), 100 deletions(-)

I certainly like the diffstat ;-)

>  struct syscon {
> +	struct device_node *np;
>  	struct regmap *regmap;
> +	struct list_head list;
>  };

Right

> @@ -68,27 +72,6 @@ struct regmap *syscon_regmap_lookup_by_compatible(const char *s)
>  }
>  EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_compatible);
>  
> -static int syscon_match_pdevname(struct device *dev, void *data)
> -{
> -	return !strcmp(dev_name(dev), (const char *)data);
> -}
> -
> -struct regmap *syscon_regmap_lookup_by_pdevname(const char *s)
> -{
> -	struct device *dev;
> -	struct syscon *syscon;
> -
> -	dev = driver_find_device(&syscon_driver.driver, NULL, (void *)s,
> -				 syscon_match_pdevname);
> -	if (!dev)
> -		return ERR_PTR(-EPROBE_DEFER);
> -
> -	syscon = dev_get_drvdata(dev);
> -
> -	return syscon->regmap;
> -}
> -EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_pdevname);

I think this can actually be left intact if that helps with clps71xx.
It could be done in a hacky way using bus_find_device_by_name()
to keep it simple, or in a somewhat nicer way by keeping the 
syscon platform_driver around for the non-DT case.


> +	regmap = regmap_init_mmio(NULL, base, &syscon_regmap_config);
> +	if (IS_ERR(regmap)) {
> +		pr_err("regmap init failed\n");
> +		return ERR_CAST(regmap);
> +	}

The last time I looked over this code, I think it was not safe to
call regmap_init_mmio() with a NULL device pointer, and we decided
that should be fixed. Have you checked whether it is ok now?

	Arnd
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