[U-Boot] [PATCH v3 16/25] riscv: Update supports_extension() to use desc from cpu driver

[Auer, Lukas]

Hi Bin,

On Tue, 2018-12-11 at 01:34 -0800, Bin Meng wrote:
> This updates supports_extension() implementation to use the desc
> string from the cpu driver whenever possible, which avoids the
> reading of misa CSR for S-mode U-Boot.
> 
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> 
> ---
> 
> Changes in v3:
> - new patch to update supports_extension() to use desc from cpu
> driver
> 
> Changes in v2: None
> 
>  arch/riscv/cpu/cpu.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> index d3c59da..704ae70 100644
> --- a/arch/riscv/cpu/cpu.c
> +++ b/arch/riscv/cpu/cpu.c
> @@ -5,8 +5,10 @@
>  
>  #include <common.h>
>  #include <cpu.h>
> +#include <dm.h>
>  #include <log.h>
>  #include <asm/csr.h>
> +#include <dm/uclass-internal.h>
>  
>  /*
>   * prior_stage_fdt_address must be stored in the data section since
> it is used
> @@ -16,7 +18,21 @@ phys_addr_t prior_stage_fdt_address
> __attribute__((section(".data")));
>  
>  static inline bool supports_extension(char ext)
>  {
> +#ifdef CONFIG_CPU
> +	struct udevice *dev;
> +	char desc[32];
> +
> +	uclass_find_first_device(UCLASS_CPU, &dev);
> +	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> +		/* skip the first 4 characters (rv32|rv64) */
> +		if (strchr(desc + 4, ext))
> +			return true;
> +	}
> +
> +	return false;
> +#else
>  	return csr_read(misa) & (1 << (ext - 'a'));

This should not be used in supervisor mode, so that we don't need a
patched BBL. I think it is better to use #elif
defined(CONFIG_RISCV_MMODE) here.

There should also be a warning message to the user if
supports_extension() does not have a way to determine the available
extensions (supervisor-mode and no CONFIG_CPU or CONFIG_CPU, but no
device found). This would help to prevent difficult-to-debug errors
caused by part of the initialization missing.

Thanks,
Lukas

> +#endif
>  }
>  
>  static int riscv_cpu_probe(void)