Re: [PATCH v4 2/5] RISC-V: Add SBI debug console helper routines

[Andrew Jones]

On Sat, Nov 18, 2023 at 09:08:56AM +0530, Anup Patel wrote:
> Let us provide SBI debug console helper routines which can be
> shared by serial/earlycon-riscv-sbi.c and hvc/hvc_riscv_sbi.c.
> 
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/sbi.h |  5 +++++
>  arch/riscv/kernel/sbi.c      | 43 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 66f3933c14f6..ee7aef5f6233 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -334,6 +334,11 @@ static inline unsigned long sbi_mk_version(unsigned long major,
>  }
>  
>  int sbi_err_map_linux_errno(int err);
> +
> +extern bool sbi_debug_console_available;
> +int sbi_debug_console_write(unsigned int num_bytes, phys_addr_t base_addr);
> +int sbi_debug_console_read(unsigned int num_bytes, phys_addr_t base_addr);
> +
>  #else /* CONFIG_RISCV_SBI */
>  static inline int sbi_remote_fence_i(const struct cpumask *cpu_mask) { return -1; }
>  static inline void sbi_init(void) {}
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 5a62ed1da453..73a9c22c3945 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -571,6 +571,44 @@ long sbi_get_mimpid(void)
>  }
>  EXPORT_SYMBOL_GPL(sbi_get_mimpid);
>  
> +bool sbi_debug_console_available;
> +
> +int sbi_debug_console_write(unsigned int num_bytes, phys_addr_t base_addr)
> +{
> +	struct sbiret ret;
> +
> +	if (!sbi_debug_console_available)
> +		return -EOPNOTSUPP;
> +
> +	if (IS_ENABLED(CONFIG_32BIT))
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE,
> +				num_bytes, lower_32_bits(base_addr),
> +				upper_32_bits(base_addr), 0, 0, 0);
> +	else
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE,
> +				num_bytes, base_addr, 0, 0, 0, 0);
> +
> +	return ret.error ? sbi_err_map_linux_errno(ret.error) : ret.value;

We can't get perfect mappings, but I wonder if we can do better than
returning ENOTSUPP for "Failed to write the byte due to I/O errors."

How about

 if (ret.error == SBI_ERR_FAILURE)
     return -EIO;

 return ret.error ? sbi_err_map_linux_errno(ret.error) : ret.value;


> +}
> +
> +int sbi_debug_console_read(unsigned int num_bytes, phys_addr_t base_addr)
> +{
> +	struct sbiret ret;
> +
> +	if (!sbi_debug_console_available)
> +		return -EOPNOTSUPP;
> +
> +	if (IS_ENABLED(CONFIG_32BIT))
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_READ,
> +				num_bytes, lower_32_bits(base_addr),
> +				upper_32_bits(base_addr), 0, 0, 0);
> +	else
> +		ret = sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_READ,
> +				num_bytes, base_addr, 0, 0, 0, 0);
> +
> +	return ret.error ? sbi_err_map_linux_errno(ret.error) : ret.value;

Same comment as above.

> +}
> +
>  void __init sbi_init(void)
>  {
>  	int ret;
> @@ -612,6 +650,11 @@ void __init sbi_init(void)
>  			sbi_srst_reboot_nb.priority = 192;
>  			register_restart_handler(&sbi_srst_reboot_nb);
>  		}
> +		if ((sbi_spec_version >= sbi_mk_version(2, 0)) &&
> +		    (sbi_probe_extension(SBI_EXT_DBCN) > 0)) {
> +			pr_info("SBI DBCN extension detected\n");
> +			sbi_debug_console_available = true;
> +		}
>  	} else {
>  		__sbi_set_timer = __sbi_set_timer_v01;
>  		__sbi_send_ipi	= __sbi_send_ipi_v01;
> -- 
> 2.34.1
>

Otherwise,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

Thanks,
drew