Subject: [PATCH 2/2] ARM: local timers: add timer support using IO mapped register

From: [email-masked] (Rohit Vaswani)
Date: Fri, 10 Aug 2012 16:37:42 -0700

Thanks for your feedback Rob.

On 8/10/2012 3:10 PM, Rob Herring wrote:
> On 08/10/2012 04:58 PM, Rohit Vaswani wrote:
>> The current arch_timer only support accessing through CP15 interface.
>> Add support for ARM processors that only support IO mapped register
>> interface
>>
>> Signed-off-by: Rohit Vaswani <[email-masked]>
>> ---
>>   .../devicetree/bindings/arm/arch_timer.txt         |    7 +
>>   arch/arm/kernel/arch_timer.c                       |  259 ++++++++++++++++----
>>   2 files changed, 223 insertions(+), 43 deletions(-)
> The original file is 360 lines. It doesn't really seem like there's a
> lot of overlap and I wonder if it is worth the extra overhead.
>
>> diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt
>> index 52478c8..1c71799 100644
>> --- a/Documentation/devicetree/bindings/arm/arch_timer.txt
>> +++ b/Documentation/devicetree/bindings/arm/arch_timer.txt
>> @@ -14,6 +14,13 @@ The timer is attached to a GIC to deliver its per-processor interrupts.
>>   
>>   - clock-frequency : The frequency of the main counter, in Hz. Optional.
>>   
>> +- irq-is-not-percpu: Specify is the timer irq is *NOT* a percpu (PPI) interrupt
>> +  In the default case i.e without this property, the timer irq is treated as a
>> +  PPI interrupt. Optional.
> The first field in the gic interrupts binding already defines this.
Is there a generic way to extract that information from the interrupts 
binding. I saw Chris Smith's patch that adds irq_is_per_cpu function. 
Perhaps we can use that once it is merged ?
>
>> +
>> +- If the node address and reg is specified, the arch_timer will try to use the memory
>> +  mapped timer. Optional.
> This timer is fundamentally different h/w. You need a new compatible string.
I think that the timer is the same, but it just has a different 
interface. Do you still think we need a new compatible string ?
>
>> +
>>   Example:
>>   
>>   	timer {
>> diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
>> index 1d0d9df..09604b7 100644
>> --- a/arch/arm/kernel/arch_timer.c
>> +++ b/arch/arm/kernel/arch_timer.c
>> @@ -18,6 +18,7 @@
>>   #include <linux/clockchips.h>
>>   #include <linux/interrupt.h>
>>   #include <linux/of_irq.h>
>> +#include <linux/of_address.h>
>>   #include <linux/io.h>
>>   
>>   #include <asm/cputype.h>
>> @@ -29,8 +30,17 @@
>>   static unsigned long arch_timer_rate;
>>   static int arch_timer_ppi;
>>   static int arch_timer_ppi2;
>> +static int is_irq_percpu;
>>   
>>   static struct clock_event_device __percpu **arch_timer_evt;
>> +static void __iomem *timer_base;
>> +
>> +struct arch_timer_operations {
>> +	void (*reg_write)(int, u32);
>> +	u32 (*reg_read)(int);
>> +	cycle_t (*get_cntpct)(void);
>> +	cycle_t (*get_cntvct)(void);
>> +};
>>   
>>   /*
>>    * Architected system timer support.
>> @@ -44,7 +54,29 @@ static struct clock_event_device __percpu **arch_timer_evt;
>>   #define ARCH_TIMER_REG_FREQ		1
>>   #define ARCH_TIMER_REG_TVAL		2
>>   
>> -static void arch_timer_reg_write(int reg, u32 val)
>> +/* Iomapped Register Offsets */
>> +#define ARCH_TIMER_CNTP_LOW_REG		0x000
>> +#define ARCH_TIMER_CNTP_HIGH_REG	0x004
>> +#define ARCH_TIMER_CNTV_LOW_REG		0x008
>> +#define ARCH_TIMER_CNTV_HIGH_REG	0x00C
>> +#define ARCH_TIMER_CTRL_REG		0x02C
>> +#define ARCH_TIMER_FREQ_REG		0x010
>> +#define ARCH_TIMER_CNTP_TVAL_REG	0x028
>> +#define ARCH_TIMER_CNTV_TVAL_REG	0x038
>> +
>> +static void timer_reg_write_mem(int reg, u32 val)
>> +{
>> +	switch (reg) {
>> +	case ARCH_TIMER_REG_CTRL:
>> +		__raw_writel(val, timer_base + ARCH_TIMER_CTRL_REG);
>> +		break;
>> +	case ARCH_TIMER_REG_TVAL:
>> +		__raw_writel(val, timer_base + ARCH_TIMER_CNTP_TVAL_REG);
>> +		break;
> This whole function seems a bit pointless as it only adds timer_base.
>
> Rob
I tried to the keep the functions similar to the cp15 interface ones. Is 
there something else you suggest doing ?

Thanks,
Rohit Vaswani

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