From mboxrd@z Thu Jan 1 00:00:00 1970 From: Samuel Ortiz Subject: Re: [RFC PATCH v5 0/1] drivers: mfd: Versatile Express SPC support Date: Wed, 17 Jul 2013 23:07:00 +0200 Message-ID: <20130717210700.GA19864@zurbaran> References: <1373990743-23106-1-git-send-email-lorenzo.pieralisi@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1373990743-23106-1-git-send-email-lorenzo.pieralisi-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Lorenzo Pieralisi Cc: Nicolas Pitre , Jon Medhurst , Pawel Moll , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Amit Kucheria , Achin Gupta , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: devicetree@vger.kernel.org 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/