Re: [PATCH v3 2/2] Allow for riscv-clock to pick up mmio address.

[Aleksa Paunovic <aleksa.paunovic@htecgroup.com>]

On 29. 4. 25. 10:52, Daniel Lezcano wrote:
> On Wed, Apr 23, 2025 at 12:17:37PM +0000, Aleksa Paunovic wrote:
>> HTEC Public
>>
>> Allow faster rdtime access via GCR.U mtime shadow register on RISC-V
>> devices. This feature can be enabled by setting GCRU_TIME_MMIO during configuration.
>>
>> Signed-off-by: Aleksa Paunovic <aleksa.paunovic@htecgroup.com>
>> ---
>>  arch/riscv/include/asm/timex.h    | 59 ++++++++++++++++++++-----------
>>  drivers/clocksource/Kconfig       | 12 +++++++
>>  drivers/clocksource/timer-riscv.c | 32 +++++++++++++++++
>>  3 files changed, 83 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> index a06697846e69..47ad6285b83a 100644
>> --- a/arch/riscv/include/asm/timex.h
>> +++ b/arch/riscv/include/asm/timex.h
>> @@ -7,31 +7,24 @@
>>  #define _ASM_RISCV_TIMEX_H
>>
>>  #include <asm/csr.h>
>> +#include <asm/mmio.h>
>> +
>> +#include <linux/jump_label.h>
>>
>>  typedef unsigned long cycles_t;
>>
>> +extern u64 __iomem *riscv_time_val;
>> +DECLARE_STATIC_KEY_FALSE(riscv_time_mmio_available);
> 
> Please keep it self-encapsulate in the timer-riscv.c
> 
>> +#define riscv_time_val riscv_time_val
> 
> why ?
>    
We decided to leave this in v4[1] for consistency with the #define riscv_time_val clint_time_val macro. Similar to the #define get_cycles get_cycles macro. Will remove in v5 if unnecessary.  

[1]
https://lore.kernel.org/linux-riscv/20250514-riscv-time-mmio-v4-0-cb0cf2922d66@htecgroup.com/

Best regards,
Aleksa Paunovic

>>  #ifdef CONFIG_RISCV_M_MODE
>>
>>  #include <asm/clint.h>
>>
>> -#ifdef CONFIG_64BIT
>> -static inline cycles_t get_cycles(void)
>> -{
>> -       return readq_relaxed(clint_time_val);
>> -}
>> -#else /* !CONFIG_64BIT */
>> -static inline u32 get_cycles(void)
>> -{
>> -       return readl_relaxed(((u32 *)clint_time_val));
>> -}
>> -#define get_cycles get_cycles
>> +#undef riscv_time_val
>>
>> -static inline u32 get_cycles_hi(void)
>> -{
>> -       return readl_relaxed(((u32 *)clint_time_val) + 1);
>> -}
>> -#define get_cycles_hi get_cycles_hi
>> -#endif /* CONFIG_64BIT */
>> +#define riscv_time_val clint_time_val
>>
>>  /*
>>   * Much like MIPS, we may not have a viable counter to use at an early point
>> @@ -46,22 +39,48 @@ static inline unsigned long random_get_entropy(void)
>>  }
>>  #define random_get_entropy()   random_get_entropy()
>>
>> -#else /* CONFIG_RISCV_M_MODE */
>> +#endif
>> +
>> +static inline long use_riscv_time_mmio(void)
>> +{
>> +       return IS_ENABLED(CONFIG_RISCV_M_MODE) ||
>> +               (IS_ENABLED(CONFIG_GCRU_TIME_MMIO) &&
>> +                static_branch_unlikely(&riscv_time_mmio_available));
>> +}
>> +
> 
> Don't use this function to branch when calling get_cycles(). Provide two
> versions of the *get_cycles* and initialize with the right one at init time.
> 
>> +#ifdef CONFIG_64BIT
>> +static inline cycles_t mmio_get_cycles(void)
>> +{
>> +       return readq_relaxed(riscv_time_val);
>> +}
>> +#else /* !CONFIG_64BIT */
>> +static inline cycles_t mmio_get_cycles(void)
>> +{
>> +       return readl_relaxed(((u32 *)riscv_time_val));
>> +}
>> +#endif /* CONFIG_64BIT */
>> +
>> +static inline u32 mmio_get_cycles_hi(void)
>> +{
>> +       return readl_relaxed(((u32 *)riscv_time_val) + 1);
>> +}
>>
>>  static inline cycles_t get_cycles(void)
>>  {
>> +       if (use_riscv_time_mmio())
>> +               return mmio_get_cycles();
>>         return csr_read(CSR_TIME);
>>  }
>>  #define get_cycles get_cycles
>>
>>  static inline u32 get_cycles_hi(void)
>>  {
>> +       if (use_riscv_time_mmio())
>> +               return mmio_get_cycles_hi();
>>         return csr_read(CSR_TIMEH);
>>  }
>>  #define get_cycles_hi get_cycles_hi
>>
>> -#endif /* !CONFIG_RISCV_M_MODE */
>> -
>>  #ifdef CONFIG_64BIT
>>  static inline u64 get_cycles64(void)
>>  {
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 487c85259967..0f2bb75564c7 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -661,6 +661,18 @@ config CLINT_TIMER
>>           This option enables the CLINT timer for RISC-V systems.  The CLINT
>>           driver is usually used for NoMMU RISC-V systems.
>>
>> +config GCRU_TIME_MMIO
>> +       bool "GCR.U timer support for RISC-V platforms"
>> +       depends on !RISCV_M_MODE && RISCV
>> +       default n
>> +       help
>> +        Access GCR.U shadow copy of the RISC-V mtime register
>> +        on platforms that provide a compatible device, instead of
>> +        reading the time CSR. Since reading the time CSR
>> +        traps to M mode on certain platforms, this may be more efficient.
>> +
>> +        If you don't know what to do here, say n.
>> +
>>  config CSKY_MP_TIMER
>>         bool "SMP Timer for the C-SKY platform" if COMPILE_TEST
>>         depends on CSKY
>> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
>> index 48ce50c5f5e6..4290e4b840f7 100644
>> --- a/drivers/clocksource/timer-riscv.c
>> +++ b/drivers/clocksource/timer-riscv.c
>> @@ -22,6 +22,7 @@
>>  #include <linux/io-64-nonatomic-lo-hi.h>
>>  #include <linux/interrupt.h>
>>  #include <linux/of_irq.h>
>> +#include <linux/of_address.h>
>>  #include <linux/limits.h>
>>  #include <clocksource/timer-riscv.h>
>>  #include <asm/smp.h>
>> @@ -32,6 +33,13 @@
>>  static DEFINE_STATIC_KEY_FALSE(riscv_sstc_available);
>>  static bool riscv_timer_cannot_wake_cpu;
>>
>> +#if defined(CONFIG_GCRU_TIME_MMIO)
>> +DEFINE_STATIC_KEY_FALSE_RO(riscv_time_mmio_available);
> 
> static DEFINE_STATIC_KEY_FALSE_RO( ... )
> 
>> +EXPORT_SYMBOL(riscv_time_mmio_available);
>> +u64 __iomem *riscv_time_val __ro_after_init;
>> +EXPORT_SYMBOL(riscv_time_val);
>> +#endif
>> +
>>  static void riscv_clock_event_stop(void)
>>  {
>>         if (static_branch_likely(&riscv_sstc_available)) {
>> @@ -203,6 +211,11 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>>         int cpuid, error;
>>         unsigned long hartid;
>>         struct device_node *child;
>> +#if defined(CONFIG_GCRU_TIME_MMIO)
>> +       u64 mmio_addr;
>> +       u64 mmio_size;
>> +       struct device_node *gcru;
>> +#endif
>>
>>         error = riscv_of_processor_hartid(n, &hartid);
>>         if (error < 0) {
>> @@ -220,6 +233,25 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>>         if (cpuid != smp_processor_id())
>>                 return 0;
>>
>> +#if defined(CONFIG_GCRU_TIME_MMIO)
>> +       gcru = of_find_compatible_node(NULL, NULL, "mti,gcru");
>> +       if (gcru) {
>> +               if (!of_property_read_reg(gcru, 0, &mmio_addr, &mmio_size)) {
>> +                       riscv_time_val = ioremap((long)mmio_addr, mmio_size);
>> +                       if (riscv_time_val) {
>> +                               pr_info("Using mmio time register at 0x%llx\n",
>> +                                       mmio_addr);
>> +                               static_branch_enable(
>> +                                       &riscv_time_mmio_available);
>> +                       } else {
>> +                               pr_warn("Unable to use mmio time at 0x%llx\n",
>> +                                       mmio_addr);
>> +                       }
>> +                       of_node_put(gcru);
>> +               }
>> +       }
>> +#endif
>> +
>>         child = of_find_compatible_node(NULL, NULL, "riscv,timer");
>>         if (child) {
>>                 riscv_timer_cannot_wake_cpu = of_property_read_bool(child,
>> --
>> 2.34.1
> 
> --
> 
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