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Date:	Fri, 19 Sep 2014 16:18:36 +0200
From:	Javier Martinez Canillas <javier@...hile0.org>
To:	Pankaj Dubey <pankaj.dubey@...sung.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Russell King <linux@....linux.org.uk>,
	vikas.sajjan@...sung.com, sunil joshi <joshi@...sung.com>,
	naushad@...sung.com, thomas.ab@...sung.com, chow.kim@...sung.com,
	Kukjin Kim <kgene.kim@...sung.com>, b29396@...escale.com,
	Li.Xiubo@...escale.com
Subject: Re: [PATCH v4] mfd: syscon: Decouple syscon interface from platform devices

Hello Pankaj,

On Fri, Sep 19, 2014 at 3:06 PM, Pankaj Dubey <pankaj.dubey@...sung.com> 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 where is can be probed and such non-DT based drivers can use
> syscon_regmap_lookup_by_pdev API and get access to regmap handles.
> Once all users of "syscon_regmap_lookup_by_pdev" migrated to DT based,
> we can completly remove platform driver of syscon, and keep only helper
> functions to get regmap handles.
>
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Suggested-by: Tomasz Figa <tomasz.figa@...il.com>
> Tested-by: Vivek Gautam <gautam.vivek@...sung.com>
> Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> ---
> 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]: https://lkml.org/lkml/2014/9/2/299
>  drivers/mfd/syscon.c |  102 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 79 insertions(+), 23 deletions(-)
>

I tested this patch on an Exynos5420 Peach Pit Chromebook and I see
that of_syscon_register() is called for the PMU system controller with
compatible string "samsung,exynos5420-pmu", "syscon" which does not
have a dedicated platform driver, so:

Tested-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>

Best regards,
Javier
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