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SubjectRe: [RFC PATCH v5 0/1] drivers: mfd: Versatile Express SPC support
Hi Lorenzo,

On Tue, Jul 16, 2013 at 05:05:42PM +0100, Lorenzo Pieralisi wrote:
> Hello,
>
> version v5 of VExpress SPC driver, please read on the changelog for major
> changes and explanations.
>
> The probing scheme is unchanged, since after trying the early platform
> devices approach it appeared that the end result was no better than the
> current one. The only clean solution relies either on changing how
> secondaries are brought up in the kernel (later than now) or enable
> early platform device registration through DT. Please check this
> thread for the related discussion:
>
> https://lists.ozlabs.org/pipermail/devicetree-discuss/2013-June/036542.html
>
> The interface was adapted to regmap and again reverted to old driver for
> the following reasons:
>
> - Power down registers locking is hairy and requires arch spinlocks in
> the MCPM back end to work properly, normal spinlocks cannot be used
> - Regmap adds unnecessary code to manage SPC since it is just a bunch of
> registers used to control power management flags, the overhead is just
> not worth it (talking about power down registers, not the vexpress config
> interface)
> - The locking scheme behind regmap requires all registers in the map
> to be protected with the same lock, which is not exactly what we want
> here
> - Given the reasons above, adding a regmap interface buys us nothing from
> a driver readability and maintainability perspective (again just talking
> about the power interface, a few registers) because for the SPC it would
> simply not be used
>
> /drivers/mfd is probably not the right place for this code as it stands (but
> probably will be when the entire driver, with DVFS and config interface, is
> complete).
Could you please elaborate on how will the SPC driver extend into an MFD
driver?

Cheers,
Samuel.

--
Intel Open Source Technology Centre
http://oss.intel.com/


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