Re: [PATCH v2] RISC-V: Check clint_time_val before use

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On Sat, 2020-09-26 at 15:51 +0530, Anup Patel wrote:
> The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> because the get_cycles() and friends are called very early from
> rand_initialize() before CLINT driver is probed. To fix this, we
> should check clint_time_val before use in get_cycles() and friends.
> 
> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> for M-mode systems")
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
> Changes since v1:
>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>    avoid hang on Kendryte K210
> ---
>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
>  drivers/clocksource/timer-clint.c |  2 +-
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..6e7b04874755 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -17,18 +17,24 @@ typedef unsigned long cycles_t;
>  #ifdef CONFIG_64BIT
>  static inline cycles_t get_cycles(void)
>  {
> -	return readq_relaxed(clint_time_val);
> +	if (clint_time_val)
> +		return readq_relaxed(clint_time_val);
> +	return 0;
>  }
>  #else /* !CONFIG_64BIT */
>  static inline u32 get_cycles(void)
>  {
> -	return readl_relaxed(((u32 *)clint_time_val));
> +	if (clint_time_val)
> +		return readl_relaxed(((u32 *)clint_time_val));
> +	return 0;
>  }
>  #define get_cycles get_cycles
>  
>  static inline u32 get_cycles_hi(void)
>  {
> -	return readl_relaxed(((u32 *)clint_time_val) + 1);
> +	if (clint_time_val)
> +		return readl_relaxed(((u32 *)clint_time_val) + 1);
> +	return 0;
>  }
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */
> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> index d17367dee02c..8dbec85979fd 100644
> --- a/drivers/clocksource/timer-clint.c
> +++ b/drivers/clocksource/timer-clint.c
> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
>  static unsigned int clint_timer_irq;
>  
>  #ifdef CONFIG_RISCV_M_MODE
> -u64 __iomem *clint_time_val;
> +u64 __iomem *clint_time_val = NULL;
>  #endif
>  
>  static void clint_send_ipi(const struct cpumask *target)

For Kendryte:

Tested-by: Damien Le Moal <damien.lemoal@wdc.com>

-- 
Damien Le Moal
Western Digital