From mboxrd@z Thu Jan  1 00:00:00 1970
From: santosh.shilimkar@ti.com (Santosh Shilimkar)
Date: Fri, 11 Jan 2013 22:30:17 +0530
Subject: [PATCHv2 08/11] arm: arch_timer: add arch_counter_set_user_access
In-Reply-To: <20130111150703.GA13717@mudshark.cambridge.arm.com>
References: <1357747640-18594-1-git-send-email-mark.rutland@arm.com>
 <1357747640-18594-9-git-send-email-mark.rutland@arm.com>
 <50F01646.4010203@ti.com>
 <20130111145451.GD19765@e106331-lin.cambridge.arm.com>
 <20130111150703.GA13717@mudshark.cambridge.arm.com>
Message-ID: <50F04521.8030204@ti.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Friday 11 January 2013 08:37 PM, Will Deacon wrote:
> On Fri, Jan 11, 2013 at 02:54:52PM +0000, Mark Rutland wrote:
>> On Fri, Jan 11, 2013 at 01:40:22PM +0000, Santosh Shilimkar wrote:
>>> So how do you expect platform to enabled the user-space access in case
>>> they want to access it for some cases.
>>
>> Unlike AArch64, at the moment we don't have the infrastructure to map this for
>> userspace accesses, so it isn't much of a problem.
>>
>> If in future we wish to map it on 32bit platforms, the arm implementation of
>> arch_counter_set_user_access can be modified to allow userspace access to
>> specific registers, and additional code would be required to actually map it
>> into the user address space, etc.
>
> I'd also add that it's not up to a platform to decide whether to expose
> this to userspace: it needs to be an architecture-wide decision. Otherwise,
> userspace becomes SoC-specific, which is a complete disaster.
>
> So, if userspace people want these available, they need to convince us to
> flip the switch. In the meantime, it should default to off so that if/when
> we do enable it we can do it in a sane manner for ARM (perhaps via the
> vectors page).
>
Thanks Will for rationale behind the change. Good to capture the 
reasoning in changelog for future reference.

Regards,
Santosh