Re: [PATCH RESEND v4 1/8] clocksource: timer-riscv: select CSR from device tree

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 17.08.21 12:10, Antony Pavlov wrote:
> barebox timer-riscv driver supports one of user counters:
> 
>   * 'cycle', counter for RDCYCLE instruction (CSR 0xc00);
>   * 'time', timer for RDTIME instruction (CSR 0xc01).
> 
> At the moment in M-mode timer-riscv uses the 'cycle' counter,
> and in S-mode timer-riscv uses the 'time' timer.
> 
> Alas picorv32 CPU core supports only the 'cycle' counter.
> VexRiscV CPU core in M-mode supports only the 'time' timer.
> 
> This patch makes it possible to use the 'time' timer
> for VexRiscV CPU in M-mode.
> 
> See also http://lists.infradead.org/pipermail/barebox/2021-May/036067.html

Comment from earlier series:

"It also changes the default for M-Mode from cycle to time.

I can't comment on whether this is ok, I just copied the logic

from Linux."

Can you say why this is ok?

> 
> Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
> ---
>  arch/riscv/dts/erizo.dtsi         |  2 ++
>  drivers/clocksource/timer-riscv.c | 24 ++++++++++++------------
>  2 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/riscv/dts/erizo.dtsi b/arch/riscv/dts/erizo.dtsi
> index 228711bd69..4eb92ae6f1 100644
> --- a/arch/riscv/dts/erizo.dtsi
> +++ b/arch/riscv/dts/erizo.dtsi
> @@ -22,6 +22,8 @@
>  
>  		timebase-frequency = <24000000>;
>  
> +		barebox,csr-cycle;
> +
>  		cpu@0 {
>  			device_type = "cpu";
>  			compatible = "cliffordwolf,picorv32", "riscv";
> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> index 5a517fe6b4..96637f988a 100644
> --- a/drivers/clocksource/timer-riscv.c
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -12,9 +12,8 @@
>  #include <clock.h>
>  #include <asm/timer.h>
>  #include <asm/csr.h>
> -#include <asm/system.h>
>  
> -static u64 notrace riscv_timer_get_count_sbi(void)
> +static u64 notrace riscv_timer_get_count_time(void)
>  {
>  	__maybe_unused u32 hi, lo;
>  
> @@ -29,7 +28,7 @@ static u64 notrace riscv_timer_get_count_sbi(void)
>  	return ((u64)hi << 32) | lo;
>  }
>  
> -static u64 notrace riscv_timer_get_count_rdcycle(void)
> +static u64 notrace riscv_timer_get_count_cycle(void)
>  {
>  	__maybe_unused u32 hi, lo;
>  
> @@ -44,24 +43,25 @@ static u64 notrace riscv_timer_get_count_rdcycle(void)
>  	return ((u64)hi << 32) | lo;
>  }
>  
> -static u64 notrace riscv_timer_get_count(void)
> -{
> -	if (riscv_mode() == RISCV_S_MODE)
> -		return riscv_timer_get_count_sbi();
> -	else
> -		return riscv_timer_get_count_rdcycle();
> -}
> -
>  static struct clocksource riscv_clocksource = {
> -	.read		= riscv_timer_get_count,
>  	.mask		= CLOCKSOURCE_MASK(64),
>  	.priority	= 100,
>  };
>  
>  static int riscv_timer_init(struct device_d* dev)
>  {
> +	struct device_node *cpu;
> +
>  	dev_dbg(dev, "running at %lu Hz\n", riscv_timebase);
>  
> +	cpu = of_find_node_by_path("/cpus");
> +
> +	if (of_property_read_bool(cpu, "barebox,csr-cycle")) {
> +		riscv_clocksource.read = riscv_timer_get_count_cycle;
> +	} else {
> +		riscv_clocksource.read = riscv_timer_get_count_time;
> +	}
> +
>  	riscv_clocksource.mult = clocksource_hz2mult(riscv_timebase, riscv_clocksource.shift);
>  
>  	return init_clock(&riscv_clocksource);
> 


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