linux-kernel - Re: [RFC 3/8] mfd:syscon: Introduce claim/read/write/release APIs

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Date:	Wed, 08 May 2013 18:42:04 +0100
From:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Arnd Bergmann <arnd@...db.de>, dong.aisheng@...aro.org,
	sameo@...ux.intel.com, Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Stuart Menefy <stuart.menefy@...com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dia.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Nicolas Pitre <nico@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Dave Martin <dave.martin@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [RFC 3/8] mfd:syscon: Introduce claim/read/write/release APIs

Thankyou for the comments.
On 08/05/13 16:01, Mark Brown wrote:
> On Wed, May 08, 2013 at 04:50:22PM +0200, Arnd Bergmann wrote:
>
>>> In many cases a single syconf register contains bits related to multiple
>>> devices, and therefore it need to be shared across multiple drivers at
>>> bit level. The same IP block can have different syscon mappings on
>>> different SOCs.
>> My feeling is that syscon is the wrong place for this functionality,
>> since regmap already handles (some of?) these issues. If you need
>> additional synchronization, it's probably best to extend regmap
>> as needed so other code besides syscon can take advantage of that
>> as well.
> This sounds like regmap_update_bits() ought to be all that's needed.

Ultimately the syscon_write use the regmap_update_bits, however we really want is the flexibility in using/referring the syscon registers/bits in both device-trees and non-device tree cases.

The reason for these APIs, is the extent of syscon usage is very high in ST set-top-box parts.

Without these new APIs, its very difficult to pass this information to
the drivers.

Thanks,
srini
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