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

Marc Zyngier
2012-08-11T10:04:36Z

Hi Rohit,

On Fri, 10 Aug 2012 14:58:41 -0700, Rohit Vaswani
<rvaswani@codeaurora.org>
wrote:
> The current arch_timer only support accessing through CP15 interface.
> Add support for ARM processors that only support IO mapped register
> interface

This is quite a departure from the current implementation, which raises a
couple of questions:
- What does CP15 ID_PFR1[19:16] report? Can we easily detect that we do
not have the CP15 interface?
- What about HYP mode? Is there any way to control the access of the
physical timer at PL1?

> Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
> ---
> .../devicetree/bindings/arm/arch_timer.txt | 7 +
> arch/arm/kernel/arch_timer.c | 259
> ++++++++++++++++----
> 2 files changed, 223 insertions(+), 43 deletions(-)
>
> 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.

Ouch! How do you specify the various interrupts for all CPUs? Do you end
up with 4 SPIs per CPU?

> +- If the node address and reg is specified, the arch_timer will try to
> use the memory
> + mapped timer. Optional.
> +
> 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);
> +};

I already have something similar in a patch series that I'd like to get
merged in 3.7, implementing support for the virtual timers (needed for
virtualisation). Have a look at:
git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git
timers-next

> /*
> * 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;
> + }
> +}
> +
> +static void timer_reg_write_cp15(int reg, u32 val)
> {
> switch (reg) {
> case ARCH_TIMER_REG_CTRL:
> @@ -58,7 +90,28 @@ static void arch_timer_reg_write(int reg, u32 val)
> isb();
> }
>
> -static u32 arch_timer_reg_read(int reg)
> +static u32 timer_reg_read_mem(int reg)
> +{
> + u32 val;
> +
> + switch (reg) {
> + case ARCH_TIMER_REG_CTRL:
> + val = __raw_readl(timer_base + ARCH_TIMER_CTRL_REG);
> + break;
> + case ARCH_TIMER_REG_FREQ:
> + val = __raw_readl(timer_base + ARCH_TIMER_FREQ_REG);
> + break;
> + case ARCH_TIMER_REG_TVAL:
> + val = __raw_readl(timer_base + ARCH_TIMER_CNTP_TVAL_REG);
> + break;
> + default:
> + BUG();
> + }
> +
> + return val;
> +}
> +
> +static u32 timer_reg_read_cp15(int reg)
> {
> u32 val;
>
> @@ -79,6 +132,103 @@ static u32 arch_timer_reg_read(int reg)
> return val;
> }
>
> +static cycle_t arch_counter_get_cntpct_mem(void)
> +{
> + u32 cvall, cvalh, thigh;
> +
> + do {
> + cvalh = __raw_readl(timer_base + ARCH_TIMER_CNTP_HIGH_REG);
> + cvall = __raw_readl(timer_base + ARCH_TIMER_CNTP_LOW_REG);
> + thigh = __raw_readl(timer_base + ARCH_TIMER_CNTP_HIGH_REG);
> + } while (cvalh != thigh);
> +
> + return ((cycle_t) cvalh << 32) | cvall;
> +}
> +
> +static cycle_t arch_counter_get_cntpct_cp15(void)
> +{
> + u32 cvall, cvalh;
> +
> + asm volatile("mrrc p15, 0, %0, %1, c14" : "=r" (cvall), "=r" (cvalh));
> +
> + return ((cycle_t) cvalh << 32) | cvall;
> +}
> +
> +static cycle_t arch_counter_get_cntvct_mem(void)
> +{
> + u32 cvall, cvalh, thigh;
> +
> + do {
> + cvalh = __raw_readl(timer_base + ARCH_TIMER_CNTV_HIGH_REG);
> + cvall = __raw_readl(timer_base + ARCH_TIMER_CNTV_LOW_REG);
> + thigh = __raw_readl(timer_base + ARCH_TIMER_CNTV_HIGH_REG);
> + } while (cvalh != thigh);
> +
> + return ((cycle_t) cvalh << 32) | cvall;
> +}
> +
> +static cycle_t arch_counter_get_cntvct_cp15(void)
> +{
> + u32 cvall, cvalh;
> +
> + asm volatile("mrrc p15, 1, %0, %1, c14" : "=r" (cvall), "=r" (cvalh));
> +
> + return ((cycle_t) cvalh << 32) | cvall;
> +}
> +
> +static struct arch_timer_operations arch_timer_ops_cp15 = {
> + .reg_read = &timer_reg_read_cp15,
> + .reg_write = &timer_reg_write_cp15,
> + .get_cntpct = &arch_counter_get_cntpct_cp15,
> + .get_cntvct = &arch_counter_get_cntvct_cp15,
> +};
> +
> +static struct arch_timer_operations arch_timer_ops_mem = {
> + .reg_read = &timer_reg_read_mem,
> + .reg_write = &timer_reg_write_mem,
> + .get_cntpct = &arch_counter_get_cntpct_mem,
> + .get_cntvct = &arch_counter_get_cntvct_mem,
> +};
> +
> +static struct arch_timer_operations *arch_specific_timer =
> &arch_timer_ops_cp15;
> +
> +static inline void arch_timer_reg_write(int reg, u32 val)
> +{
> + arch_specific_timer->reg_write(reg, val);
> +}
> +
> +static inline u32 arch_timer_reg_read(int reg)
> +{
> + return arch_specific_timer->reg_read(reg);
> +}
> +
> +static inline cycle_t arch_counter_get_cntpct(void)
> +{
> + return arch_specific_timer->get_cntpct();
> +}
> +
> +static inline cycle_t arch_counter_get_cntvct(void)
> +{
> + return arch_specific_timer->get_cntvct();
> +}
> +
> +static u32 notrace arch_counter_get_cntvct32(void)
> +{
> + cycle_t cntvct = arch_counter_get_cntpct();
> +
> + /*
> + * The sched_clock infrastructure only knows about counters
> + * with at most 32bits. Forget about the upper 24 bits for the
> + * time being...
> + */
> + return (u32)(cntvct & (u32)~0);
> +}
> +
> +static cycle_t arch_counter_read(struct clocksource *cs)
> +{
> + return arch_counter_get_cntpct();
> +}
> +
> static irqreturn_t arch_timer_handler(int irq, void *dev_id)
> {
> struct clock_event_device *evt = *(struct clock_event_device
**)dev_id;
> @@ -167,7 +317,9 @@ static int arch_timer_available(void)
> {
> unsigned long freq;
>
> - if (!local_timer_is_architected())
> + if (timer_base)
> + arch_specific_timer = &arch_timer_ops_mem;
> + else if (!local_timer_is_architected())
> return -ENXIO;
>
> if (arch_timer_rate == 0) {
> @@ -188,41 +340,6 @@ static int arch_timer_available(void)
> return 0;
> }
>
> -static inline cycle_t arch_counter_get_cntpct(void)
> -{
> - u32 cvall, cvalh;
> -
> - asm volatile("mrrc p15, 0, %0, %1, c14" : "=r" (cvall), "=r" (cvalh));
> -
> - return ((cycle_t) cvalh << 32) | cvall;
> -}
> -
> -static inline cycle_t arch_counter_get_cntvct(void)
> -{
> - u32 cvall, cvalh;
> -
> - asm volatile("mrrc p15, 1, %0, %1, c14" : "=r" (cvall), "=r" (cvalh));
> -
> - return ((cycle_t) cvalh << 32) | cvall;
> -}
> -
> -static u32 notrace arch_counter_get_cntvct32(void)
> -{
> - cycle_t cntvct = arch_counter_get_cntvct();
> -
> - /*
> - * The sched_clock infrastructure only knows about counters
> - * with at most 32bits. Forget about the upper 24 bits for the
> - * time being...
> - */
> - return (u32)(cntvct & (u32)~0);
> -}
> -
> -static cycle_t arch_counter_read(struct clocksource *cs)
> -{
> - return arch_counter_get_cntpct();
> -}
> -
> static struct clocksource clocksource_counter = {
> .name = "arch_sys_counter",
> .rating = 400,
> @@ -262,8 +379,12 @@ static int __init arch_timer_register(void)
>
> clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>
> - err = request_percpu_irq(arch_timer_ppi, arch_timer_handler,
> + if (is_irq_percpu)
> + err = request_percpu_irq(arch_timer_ppi, arch_timer_handler,
> "arch_timer", arch_timer_evt);
> + else
> + err = request_irq(arch_timer_ppi, arch_timer_handler, 0,
> + "arch_timer", arch_timer_evt);

So you end up enabling the interrupt earlier than expected. Are you sure
this is safe?

> if (err) {
> pr_err("arch_timer: can't register interrupt %d (%d)\n",
> arch_timer_ppi, err);
> @@ -271,8 +392,13 @@ static int __init arch_timer_register(void)
> }
>
> if (arch_timer_ppi2) {
> - err = request_percpu_irq(arch_timer_ppi2, arch_timer_handler,
> - "arch_timer", arch_timer_evt);
> + if (is_irq_percpu)
> + err = request_percpu_irq(arch_timer_ppi2,
> + arch_timer_handler, "arch_timer",
> + arch_timer_evt);
> + else
> + err = request_irq(arch_timer_ppi2, arch_timer_handler,
> + 0, "arch_timer", arch_timer_evt);
> if (err) {
> pr_err("arch_timer: can't register interrupt %d (%d)\n",
> arch_timer_ppi2, err);
> @@ -314,10 +440,40 @@ static const struct of_device_id
> arch_timer_of_match[] __initconst = {
> {},
> };
>
> +static int __init arch_timer_base_init(void)
> +{
> + struct device_node *np;
> +
> + if (!timer_base) {
> + np = of_find_matching_node(NULL, arch_timer_of_match);
> + if (!np) {
> + pr_err("arch_timer: can't find DT node\n");
> + return -ENODEV;
> + }
> +
> + if (of_get_address(np, 0, NULL, NULL)) {
> + timer_base = of_iomap(np, 0);
> + if (!timer_base) {
> + pr_err("arch_timer: cant map timer base\n");
> + return -ENOMEM;
> + }
> + }
> + }
> +
> + return 0;
> +}
> +
> +static inline void __init arch_timer_base_free(void)
> +{
> + if (timer_base)
> + iounmap(timer_base);
> +}
> +
> int __init arch_timer_of_register(void)
> {
> struct device_node *np;
> u32 freq;
> + int ret;
>
> np = of_find_matching_node(NULL, arch_timer_of_match);
> if (!np) {
> @@ -331,20 +487,37 @@ int __init arch_timer_of_register(void)
>
> arch_timer_ppi = irq_of_parse_and_map(np, 0);
> arch_timer_ppi2 = irq_of_parse_and_map(np, 1);
> +
> + ret = arch_timer_base_init();
> + if (ret)
> + return ret;
> +
> + is_irq_percpu = !(of_property_read_bool(np, "irq-is-not-percpu"));
> +
> pr_info("arch_timer: found %s irqs %d %d\n",
> np->name, arch_timer_ppi, arch_timer_ppi2);
>
> - return arch_timer_register();
> + ret = arch_timer_register();
> + if (ret)
> + arch_timer_base_free();
> +
> + return ret;
> }
>
> int __init arch_timer_sched_clock_init(void)
> {
> int err;
>
> - err = arch_timer_available();
> + err = arch_timer_base_init();
> if (err)
> return err;
>
> + err = arch_timer_available();
> + if (err) {
> + arch_timer_base_free();
> + return err;
> + }
> +
> setup_sched_clock(arch_counter_get_cntvct32, 32, arch_timer_rate);
> return 0;
> }

--
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