linux-kernel - Re: [PATCH 18/20] clocksource / acpi: Add macro CLOCKSOURCE_ACPI

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Date:	Wed, 22 Jan 2014 16:47:28 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-kernel@...ts.linaro.org
Cc:	Mark Rutland <mark.rutland@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rob Herring <robh@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Olof Johansson <olof@...om.net>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>
Subject: Re: [PATCH 18/20] clocksource / acpi: Add macro CLOCKSOURCE_ACPI_DECLARE

On Wednesday 22 January 2014 15:17:49 Mark Rutland wrote:
> Except for the fact that some timers / clocksources that we already have
> in 32-bit land will likely be reused in 64-bit SoC designs. People will
> want to use the same driver for both 32-bit and 64-bit kernels, and thus
> we need CLOCKSOURCE_OF_DECLARE in 64-bit kernels.
> 
> Those platforms which will have ACPI will likely reuse existing timer IP
> blocks, and will want to make minimal changes to the driver, which will
> likely be using CLOCKSOURCE_OF_DECLARE. We can't change these to
> platform drivers or we can break existing systems because the timers
> will be registered too late.
> 
> I don't see how we can share drivers between 32-bit and 64-bit kernels
> without sharing a common driver model, and I think it makes sense to
> have some uniformity across drivers (i.e. always use
> CLOCKSOURCE_*_DECLARE rather than sometimes using platform drivers).

This still sounds like speculation. I would defer this change until
we actually have a platform that needs it.

The platforms that would reuse a lot of IP blocks are most likely
embedded systems and /not/ server hardware following some strict
specification, so they wouldn't use ACPI.

	Arnd
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