linux-kernel - Re: [PATCH v4 1/5] ARM/ARM64: arch_timer: add macros for bits in control register

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Date:	Tue, 27 Aug 2013 16:19:04 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Will Deacon <Will.Deacon@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v4 1/5] ARM/ARM64: arch_timer: add macros for bits in
 control register

On 27/08/13 15:52, Catalin Marinas wrote:
> On Tue, Aug 27, 2013 at 12:37:38PM +0100, Sudeep KarkadaNagesha wrote:
>> On 27/08/13 12:21, Catalin Marinas wrote:
>>> On Fri, Aug 23, 2013 at 05:19:05PM +0100, Sudeep KarkadaNagesha wrote:
>>>> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>>>>
>>>> Add macros to describe the bitfields in the ARM architected timer
>>>> control register to make code easy to understand.
>>>>
>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>> Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>>>> Reviewed-by: Will Deacon <will.deacon@....com>
>>>> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>>>> ---
>>>>  arch/arm/include/asm/arch_timer.h    |  9 +++++++--
>>>>  arch/arm64/include/asm/arch_timer.h  | 12 ++++++++----
>>>>  include/clocksource/arm_arch_timer.h |  8 ++++++++
>>>>  3 files changed, 23 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
>>>> index e406d57..9ef74da 100644
>>>> --- a/arch/arm/include/asm/arch_timer.h
>>>> +++ b/arch/arm/include/asm/arch_timer.h
>>>> @@ -95,8 +95,13 @@ static inline void arch_counter_set_user_access(void)
>>>>  
>>>>  	asm volatile("mrc p15, 0, %0, c14, c1, 0" : "=r" (cntkctl));
>>>>  
>>>> -	/* disable user access to everything */
>>>> -	cntkctl &= ~((3 << 8) | (7 << 0));
>>>> +	/* Disable user access to both physical/virtual counters/timers. */
>>>> +	/* Also disable virtual event stream */
>>>> +	cntkctl &= ~(ARCH_TIMER_USR_PT_ACCESS_EN
>>>> +			| ARCH_TIMER_USR_VT_ACCESS_EN
>>>> +			| ARCH_TIMER_VIRT_EVT_EN
>>>> +			| ARCH_TIMER_USR_VCT_ACCESS_EN
>>>> +			| ARCH_TIMER_USR_PCT_ACCESS_EN);
>>>>  
>>>>  	asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
>>>>  }
>>>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>>>> index 98abd47..00b09d0 100644
>>>> --- a/arch/arm64/include/asm/arch_timer.h
>>>> +++ b/arch/arm64/include/asm/arch_timer.h
>>>> @@ -101,12 +101,16 @@ static inline void arch_counter_set_user_access(void)
>>>>  {
>>>>  	u32 cntkctl;
>>>>  
>>>> -	/* Disable user access to the timers and the physical counter. */
>>>>  	asm volatile("mrs	%0, cntkctl_el1" : "=r" (cntkctl));
>>>> -	cntkctl &= ~((3 << 8) | (1 << 0));
>>>>  
>>>> -	/* Enable user access to the virtual counter and frequency. */
>>>> -	cntkctl |= (1 << 1);
>>>> +	/* Disable user access to the timers and the physical counter. */
>>>> +	cntkctl &= ~(ARCH_TIMER_USR_PT_ACCESS_EN
>>>> +			| ARCH_TIMER_USR_VT_ACCESS_EN
>>>> +			| ARCH_TIMER_USR_PCT_ACCESS_EN);
>>>> +
>>>> +	/* Enable user access to the virtual counter. */
>>>> +	cntkctl |= ARCH_TIMER_USR_VCT_ACCESS_EN;
>>>> +
>>>>  	asm volatile("msr	cntkctl_el1, %0" : : "r" (cntkctl));
>>>
>>> For consistency with arm, I think we should also disable the event
>>> stream explicitly here.
>>>
>> Yes it's done. In PATCH 3/5, a new function arch_timer_evtstrm_config is
>> added which is always called(PATCH 4/5). It's either enabled or disabled
>> explicitly based on config option for event stream.
> 
> OK, just that in this patch arm and arm64 had different settings with
> regards to the event stream.
> 
Yes correct but that's how it is currently. This patch is not modifying
anything functional, just adding macros.

> BTW, can we not avoid clearing the event stream via the
> arch_timer_evtstrm_config(false) and always assume the default as
> disabled? Do you ever go back into low power mode with event stream
> disabled and come back with it enabled?
> 
Yes that can be done. But since the cold/warm reset involves other
firmware which can modify that bit, IMO it would be better to do it
explicitly as CONFIG_ARM_ARCH_TIMER_EVTSTREAM=n has to ensure its
disabled. Though I don't have a strong opinion on this, the reason for
my inclination towards explicit disable is because of platform firmware.
e.g. on V2P_CA15_A7/TC2 bootmon/secure firmware enables this bit based
on some settings in board.txt
I can remove as it's disabled on reset(ARM ARM says its reset value is
0) but with the assumption that other firmware don't modify that bit.

Regards,
Sudeep




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