Re: [kvm-unit-tests PATCH V4 4/5] lib/powerpc: Implement generic delay function for use in unit tests

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On 17.08.2016 08:48, Suraj Jitindar Singh wrote:
> It would be nice if we had a generic delay function which could be used
> in unit tests, add one.
> 
> Add the variable tb_hz used to store the time base frequency which is read
> from the device tree on setup.
> 
> Add functions mdelay, udelay and delay in processor.c to delay for a given
> number of milliseconds, microseconds and time base ticks respectively.
> 
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> ---
> 
> Change Log:
> 
> V2 -> V3:
> 	- Add patch to series
> V3 -> V4:
> 	- Reword sleep->delay
> 	- Move cpu_relax to asm-generic/barrier.h
> 	- Add assert to catch when delay fns called with too large values
> ---
>  lib/asm-generic/barrier.h   |  4 ++++
>  lib/powerpc/asm/processor.h | 19 +++++++++++++++++++
>  lib/powerpc/asm/setup.h     |  2 ++
>  lib/powerpc/processor.c     | 20 ++++++++++++++++++++
>  lib/powerpc/setup.c         |  7 +++++++
>  5 files changed, 52 insertions(+)
> 
> diff --git a/lib/asm-generic/barrier.h b/lib/asm-generic/barrier.h
> index 12ae782..6a990ff 100644
> --- a/lib/asm-generic/barrier.h
> +++ b/lib/asm-generic/barrier.h
> @@ -28,4 +28,8 @@
>  #define smp_wmb()	wmb()
>  #endif
>  
> +#ifndef cpu_relax
> +#define cpu_relax()	asm volatile ("":::"memory")
> +#endif
> +
>  #endif /* _ASM_BARRIER_H_ */
> diff --git a/lib/powerpc/asm/processor.h b/lib/powerpc/asm/processor.h
> index 09692bd..ac001e1 100644
> --- a/lib/powerpc/asm/processor.h
> +++ b/lib/powerpc/asm/processor.h
> @@ -1,6 +1,7 @@
>  #ifndef _ASMPOWERPC_PROCESSOR_H_
>  #define _ASMPOWERPC_PROCESSOR_H_
>  
> +#include <libcflat.h>
>  #include <asm/ptrace.h>
>  
>  #ifndef __ASSEMBLY__
> @@ -8,4 +9,22 @@ void handle_exception(int trap, void (*func)(struct pt_regs *, void *), void *);
>  void do_handle_exception(struct pt_regs *regs);
>  #endif /* __ASSEMBLY__ */
>  
> +static inline uint64_t get_tb(void)
> +{
> +	uint64_t tb;
> +
> +	asm volatile ("mfspr %[tb],268" : [tb] "=r" (tb));
> +
> +	return tb;
> +}
> +
> +extern void delay(uint64_t cycles);
> +extern void udelay(uint64_t us);
> +
> +static inline void mdelay(uint64_t ms)
> +{
> +	while (ms--)
> +		udelay(1000);
> +}
> +
>  #endif /* _ASMPOWERPC_PROCESSOR_H_ */
> diff --git a/lib/powerpc/asm/setup.h b/lib/powerpc/asm/setup.h
> index b1e1e5a..23b4156 100644
> --- a/lib/powerpc/asm/setup.h
> +++ b/lib/powerpc/asm/setup.h
> @@ -11,6 +11,8 @@
>  extern u32 cpus[NR_CPUS];
>  extern int nr_cpus;
>  
> +extern uint64_t tb_hz;
> +
>  #define NR_MEM_REGIONS		8
>  #define MR_F_PRIMARY		(1U << 0)
>  struct mem_region {
> diff --git a/lib/powerpc/processor.c b/lib/powerpc/processor.c
> index a78bc3c..a28f2f0 100644
> --- a/lib/powerpc/processor.c
> +++ b/lib/powerpc/processor.c
> @@ -5,6 +5,8 @@
>  #include <libcflat.h>
>  #include <asm/processor.h>
>  #include <asm/ptrace.h>
> +#include <asm/setup.h>
> +#include <asm/barrier.h>
>  
>  static struct {
>  	void (*func)(struct pt_regs *, void *data);
> @@ -36,3 +38,21 @@ void do_handle_exception(struct pt_regs *regs)
>  	printf("unhandled cpu exception 0x%lx\n", regs->trap);
>  	abort();
>  }
> +
> +void delay(uint64_t cycles)
> +{
> +	uint64_t start = get_tb();
> +	/*
> +	 * Pretty unlikely unless your server has been on for, or you want to
> +	 * delay for, over 1000 years, but still.
> +	 */
> +	assert(cycles < (UINT64_MAX - start));
> +	while ((get_tb() - start) < cycles)

You could drop the parentheses around "get_tb() - start" ...

> +		cpu_relax();
> +}
> +
> +void udelay(uint64_t us)
> +{
> +	assert(us < (UINT64_MAX / tb_hz));
> +	delay((us * tb_hz) / 1000000);

... and around "us * tb_hz".

> +}
> diff --git a/lib/powerpc/setup.c b/lib/powerpc/setup.c
> index e3d2afa..65bedf5 100644
> --- a/lib/powerpc/setup.c
> +++ b/lib/powerpc/setup.c
> @@ -24,6 +24,7 @@ extern void setup_args_progname(const char *args);
>  
>  u32 cpus[NR_CPUS] = { [0 ... NR_CPUS-1] = (~0U) };
>  int nr_cpus;
> +uint64_t tb_hz;
>  
>  struct mem_region mem_regions[NR_MEM_REGIONS];
>  phys_addr_t __physical_start, __physical_end;
> @@ -72,6 +73,12 @@ static void cpu_set(int fdtnode, u32 regval, void *info)
>  		data = (u32 *)prop->data;
>  		params->dcache_bytes = fdt32_to_cpu(*data);
>  
> +		prop = fdt_get_property(dt_fdt(), fdtnode,
> +					"timebase-frequency", NULL);
> +		assert(prop != NULL);
> +		data = (u32 *)prop->data;
> +		tb_hz = fdt32_to_cpu(*data);
> +
>  		read_common_info = true;
>  	}
>  }

Two minor cosmetic nits, patch already looks also fine to me as it
currently is, so:

Reviewed-by: Thomas Huth <thuth@xxxxxxxxxx>

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