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Date:	Tue, 30 Sep 2014 09:09:22 -0700
From:	Doug Anderson <>
To:	Pankaj Dubey <>
Cc:	"" <>,
	linux-samsung-soc <>,
	Arnd Bergmann <>,,
	Lee Jones <>,,
	Tomasz Figa <>,
	Russell King <>,
	VIKAS SAJJAN C <>,, Thomas P Abraham <>,
	Kukjin Kim <>,,, Stephen Warren <>
Subject: Re: [PATCH v7] mfd: syscon: Decouple syscon interface from platform devices


On Tue, Sep 30, 2014 at 1:35 AM, Pankaj Dubey <> wrote:
> Currently a syscon entity can be only registered directly through a
> platform device that binds to a dedicated syscon driver. However in
> certain use cases it is desirable to make a device used with another
> driver a syscon interface provider.
> 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.
> In case of DT based platforms, 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 keep
> a list of such syscon objects along with syscon provider device_nodes
> and regmap handles.
> For non-DT based platforms, this patch keeps syscon platform driver
> structure so that syscon can be probed and such non-DT based drivers
> can use syscon_regmap_lookup_by_pdev API and access regmap handles.
> Once all users of "syscon_regmap_lookup_by_pdev" migrated to DT based,
> we can completely remove platform driver of syscon, and keep only helper
> functions to get regmap handles.
> Suggested-by: Arnd Bergmann <>
> Suggested-by: Tomasz Figa <>
> Tested-by: Vivek Gautam <>
> Tested-by: Javier Martinez Canillas <>
> Signed-off-by: Pankaj Dubey <>
> Reviewed-by: Arnd Bergmann <>
> Tested-by: Heiko Stuebner <>
> Reviewed-by: Heiko Stuebner <>
> ---
> Patch v6 and related discussions can be found here [1].
> Change since v5:
>  - Addressed review comments from "Heiko Stuebner".
>  - Updated commit description.
>  - Including Arnd's and Heiko's Reviewed-by.
> Change since v5:
>  - Dropping creation of dummy platform device in of_syscon_register.
>  - As we are changing syscon to decouple from platform_device, creation of
>    dummy platform_device does not look good option, and as suggested by Arnd,
>    I made another attempt so that regmap_mmio_init API should work with NULL
>    dev pointer itself. Since regmap needs to know about Syscon device node
>    properties so let's parse device node of syscon in syscon itself for any
>    such properties and using regmap_config parameter pass all such information
>    to regmap. Other concern of crashes due to NULL dev pointer in regmap already
>    addressed in separate patches of regmap. Please see [2] and [3].
> Changes since v4:
>  - Addressed Tomasz Figa's comments for v4.
>  - Added error handing in of_syscon_register function.
>  - Using devm_regmap_init_mmio instead of regmap_init_mmio.
> Changes since v3:
>  - Addressed Arnd's comment for v2.
>  - Updated of_syscon_register for adding dev pointer in regmap_init_mmio.
>  - For early users created dummy platform device.
> Changes since v2:
>  - Added back platform device support from syscon, with one change that
>    syscon will not be probed for DT based platform.
>  - Added back syscon_regmap_lookup_by_pdevname API so that non-DT base
>    users of syscon will not be broken.
>  - Removed unwanted change in syscon.h.
>  - Modified Signed-off-by list, added Suggested-by of Tomasz Figa and
>    Arnd Bergmann.
>  - Added Tested-by of Vivek Gautam for testing on Exynos platform.
> 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.
> [1]:
> [2]:
> [3]:
>  drivers/mfd/syscon.c |   96 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 74 insertions(+), 22 deletions(-)

You probably already have enough tags, but just in case.  ;)  On an
rk3288-based system (this patch backported to 3.14):

Tested-by: Doug Anderson <>
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