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

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

On 31.08.21 06:07, Antony Pavlov wrote:
> On Mon, 23 Aug 2021 14:08:52 +0200
> Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
> 
> Hi Ahmad!
> 
>> 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?
> 
> v4 patch removes riscv_mode() mention from timer-riscv code
> so timer-riscv uses the 'time' timer by default disregarding
> M-mode or S-mode is used.
> 
> I suppose that the 'time' timer is "more popular" than
> the 'cycle' counter.
> So IMHO it is ok to use "more popular" feature by default.

Ok. We'll see if something breaks.

>>> Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>

Acked-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

>>> ---
>>>  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);
>>>
>>
>>
>> -- 
>> Pengutronix e.K.                           |                             |
>> Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
>> 31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
>> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
> 
> 


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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