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Message-ID: <CAPz6YkVeE825gaZPyhDTX91v+vsbFSp+Wz4xT1WAKdtivpDnrQ@mail.gmail.com>
Date: Mon, 29 Sep 2014 12:16:06 -0700
From: Sonny Rao <sonnyrao@...omium.org>
To: Mark Rutland <mark.rutland@....com>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"dianders@...omium.org" <dianders@...omium.org>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
Sudeep Holla <Sudeep.Holla@....com>,
Olof Johansson <olof@...om.net>,
Thomas Gleixner <tglx@...utronix.de>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Will Deacon <Will.Deacon@....com>,
Catalin Marinas <Catalin.Marinas@....com>,
Russell King <linux@....linux.org.uk>,
Stephen Boyd <sboyd@...eaurora.org>,
Marc Zyngier <Marc.Zyngier@....com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] clocksource: arch_timer: Fix code to use physical
timers when requested
On Fri, Sep 26, 2014 at 2:47 AM, Mark Rutland <mark.rutland@....com> wrote:
> Hi Sonny,
>
> Apologies for the delay in replying, I'd hoped to cover this at Connect,
> but we didn't seem to get the time, and since I've been back in the UK
> it slipped my mind.
Hi Mark, no problem, thanks for following up.
>
> On Thu, Sep 11, 2014 at 11:18:15PM +0100, Sonny Rao wrote:
>> This is a bug fix for using physical arch timers when
>> the arch_timer_use_virtual boolean is false. It restores the
>> arch_counter_get_cntpct() function after removal in
>>
>> 0d651e4e "clocksource: arch_timer: use virtual counters"
>
> Given we cannot get firmware involved, I am happy to use the physical
> cp15 counters when we can't guarantee the value of CNTVOFF.
>
>> and completes the implementation of memory mapped access for physical
>> timers, so if a system is trying to use physical timers, it will
>> function properly.
>
> I don't see why we need to change the MMIO timers. Those are global
> rather than per-cpu, aren't turned off when CPUs go down (or they'd be
> useless), and we only use a single frame, so I don't see why the value
> of the virtual offset should matter.
>
> Additionally, the CP15 and MMIO timers could be configured separately
> w.r.t. timer and counter access, and for the MMIO timers we can
> determine which we can access by reading a register.
>
> I do not think the selection of physical/virtual timers should be shared
> by the CP15 and MMIO timers.
Ok, I see what you're saying. I'll remove the physical memory mapped
access code and re-post.
> Mark.
>
>>
>> We need this on certain ARMv7 systems which are architected like this:
>>
>> * The firmware doesn't know and doesn't care about hypervisor mode and
>> we don't want to add the complexity of hypervisor there.
>>
>> * The firmware isn't involved in SMP bringup or resume.
>>
>> * The ARCH timer come up with an uninitialized offset between the
>> virtual and physical counters. Each core gets a different random
>> offset.
>>
>> * The device boots in "Secure SVC" mode.
>>
>> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
>> CNTHCTL.PL1PCTEN (both default to 1 at reset)
>>
>> One example of such as system is RK3288 where it is much simpler to
>> use the physical counter since there's nobody managing the offset and
>> each time a core goes down and comes back up it will get reinitialized
>> to some other random value.
>>
>> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
>> Acked-by: Olof Johansson <olof@...om.net>
>> ---
>> v2: Add fixes tag to commit message, cc stable, copy Doug's
>> description of the systems which need this in commit message.
>> ---
>> arch/arm/include/asm/arch_timer.h | 9 +++++++++
>> arch/arm64/include/asm/arch_timer.h | 10 ++++++++++
>> drivers/clocksource/arm_arch_timer.c | 30 ++++++++++++++++++++++++++----
>> 3 files changed, 45 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
>> index 0704e0c..e72aa4d 100644
>> --- a/arch/arm/include/asm/arch_timer.h
>> +++ b/arch/arm/include/asm/arch_timer.h
>> @@ -78,6 +78,15 @@ static inline u32 arch_timer_get_cntfrq(void)
>> return val;
>> }
>>
>> +static inline u64 arch_counter_get_cntpct(void)
>> +{
>> + u64 cval;
>> +
>> + isb();
>> + asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
>> + return cval;
>> +}
>> +
>> static inline u64 arch_counter_get_cntvct(void)
>> {
>> u64 cval;
>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>> index 9400596..58657c4 100644
>> --- a/arch/arm64/include/asm/arch_timer.h
>> +++ b/arch/arm64/include/asm/arch_timer.h
>> @@ -135,6 +135,16 @@ static inline void arch_timer_evtstrm_enable(int divider)
>> #endif
>> }
>>
>> +static inline u64 arch_counter_get_cntpct(void)
>> +{
>> + u64 cval;
>> +
>> + isb();
>> + asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
>> +
>> + return cval;
>> +}
>> +
>> static inline u64 arch_counter_get_cntvct(void)
>> {
>> u64 cval;
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index 5163ec1..ad723cb 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -30,6 +30,8 @@
>> #define CNTTIDR 0x08
>> #define CNTTIDR_VIRT(n) (BIT(1) << ((n) * 4))
>>
>> +#define CNTPCT_LO 0x00
>> +#define CNTPCT_HI 0x04
>> #define CNTVCT_LO 0x08
>> #define CNTVCT_HI 0x0c
>> #define CNTFRQ 0x10
>> @@ -386,6 +388,19 @@ static u64 arch_counter_get_cntvct_mem(void)
>> return ((u64) vct_hi << 32) | vct_lo;
>> }
>>
>> +static u64 arch_counter_get_cntpct_mem(void)
>> +{
>> + u32 pct_lo, pct_hi, tmp_hi;
>> +
>> + do {
>> + pct_hi = readl_relaxed(arch_counter_base + CNTPCT_HI);
>> + pct_lo = readl_relaxed(arch_counter_base + CNTPCT_LO);
>> + tmp_hi = readl_relaxed(arch_counter_base + CNTPCT_HI);
>> + } while (pct_hi != tmp_hi);
>> +
>> + return ((u64) pct_hi << 32) | pct_lo;
>> +}
>> +
>> /*
>> * Default to cp15 based access because arm64 uses this function for
>> * sched_clock() before DT is probed and the cp15 method is guaranteed
>> @@ -429,10 +444,17 @@ static void __init arch_counter_register(unsigned type)
>> u64 start_count;
>>
>> /* Register the CP15 based counter if we have one */
>> - if (type & ARCH_CP15_TIMER)
>> - arch_timer_read_counter = arch_counter_get_cntvct;
>> - else
>> - arch_timer_read_counter = arch_counter_get_cntvct_mem;
>> + if (type & ARCH_CP15_TIMER) {
>> + if (arch_timer_use_virtual)
>> + arch_timer_read_counter = arch_counter_get_cntvct;
>> + else
>> + arch_timer_read_counter = arch_counter_get_cntpct;
>> + } else {
>> + if (arch_timer_use_virtual)
>> + arch_timer_read_counter = arch_counter_get_cntvct_mem;
>> + else
>> + arch_timer_read_counter = arch_counter_get_cntpct_mem;
>> + }
>>
>> start_count = arch_timer_read_counter();
>> clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>> --
>> 1.8.3.2
>>
>>
> --
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